It’s probably safe to say that anyone that has played any standard games has encountered some house rules, where the play of the game is changed in some way to fit the standards of the players. If you’ve ever played Monopoly, then you’ve probably played with house rules that either ignore the auctioning of property off or that make it so that taxes go into the middle to be collected by the person that lands on Free Parking. Any game from tabletop roleplaying to beer pong can see the inclusion of house rules to make the game seem either more balanced or more fun.
Often, house ruling in one direction (balance or fun) can cause the game to tip out of skew in the other direction. Taking the example of the auction rules in Monopoly, we can see how trying to make the game more balanced can make it far less enjoyable. When you remove the auction it makes it so that everyone has an equal chance to get a property based on luck and doesn’t require competing against the other players for a given property. While that might be more balanced, it essentially turns Monopoly into a game that might as well be playing itself as almost all meaningful choice is removed from the equation and makes it so that you aren’t engaged at all when it isn’t your turn. This is the type of house rule you would want to avoid.
However, house rules can also often hide some game breaking consequences when trying to make the game more fun. The classic example of this is the Wizard in the older edition D&D games that used to be only capable of learning new spells from a teacher or a scroll. A lot of gamers felt this was too restrictive and decided to house rule away the learning requirements and many also did away with spell components and most other gating mechanisms. While this certainly made the class more fun for the person playing it, it also made it so that it had so many options of combinations of spells that it made the class far more powerful than originally intended.
All of that being said, house ruling something is a great way to accommodate the needs that you might have in your gaming group. Let’s say that every time you get into combat while playing, the fights end up taking far too long and become boring once it becomes certain that they will win but they still have to slog through the rest of the enemies. Creating house rules that lower monster health, increase player damage, or reduce the number of enemies that show up can all be ways to make it so that your players stay engaged and having fun. The important thing is to never be married to a house rule until you’ve seen it in play a few times. As previously stated, sometimes there can be unknown consequences to changing a rule.
Games often have a lot of ways, big and small, that they can be adjusted to better suit what you want to get out of them. The amount of little levers that you can adjust make it so that if one way doesn’t work or causes some sort of imbalance in the game, you can try to tweak something else or change the degree to which you changed it. If you are having an issue with a game being too short but the first thing you tried to change didn’t work, that doesn’t mean that there aren’t other ways to come at the problem. Even seemingly large problems might be fixed with just tiny changes to one part of the game.

You take the blue pill, you go back to playing rules as written. You take the red pill, you stay in Wonderland and I show you my 300 page work in progress to convert Rifts to a d10 system.
A lot of times, a house rule will rise organically while playing. One or more people will point out some issue they see, the rest will either agree or disagree, and a fix will be put in place. This usually makes it the best way to get that rule to actually be accepted and used. If someone just starts telling you that they want to change how a game works even though you think it is balanced just fine, it can be hard to accept that. After all, most of us aren’t professional game designers and it can seem a little egotistical to think that we know exactly how to change a game for the better. Even if we can pinpoint a flaw in something, it’s one thing to be able to tell that a book is poorly written and quite another to write one yourself. Having everyone on board for a change at least means that nobody ends up being blamed for unforeseen issues.
Another thing to keep in mind is at the point at which house ruling something is just not going to cut it anymore. If you are playing a game with a myriad of problems such that you have a laundry list of personal rules to make it playable, maybe you should just not be playing it. For example, the Exalted 2nd Edition RPG rules were so imbalanced that people started making more and more rules to try to fix it such that there came about an Exalted 2.5 that was almost an entire rework of the game made by people that weren’t the original creators. No game is so unique that you can’t find some form of what you like about it in some other game if it is unplayable. You should be able to find something whether it’s playing with the same setting in a different system, like porting over Exalted to the Fate system, or finding a game with a similar style but with different interactions, like going from Apples to Apples to Cards Against Humanity.
While I have been stressing all the possible things that make be an issue when using a house rule, I want to make it clear that I personally think they are great. One of the things I love about games is that you can easily go ahead and change the experience to suit you. You want to make Go Fish into a drinking game? Sounds great! Want to turn D&D into a game about a group of paladins experiencing love, romance, and heartbreak? Time to run Jane Austen’s Sense Evil and Sensibility! Did I include this last paragraph just to make that incredibly shitty joke? You bet your ass I did! So get out there, play some games, change some rules, and figure out what works best for your players.
I would play sense evil and sensebility
Forbidden love between paladins who took vows of chastity! And of different gods too! Oh my! I have the vapors *faints*