The reason I edit is to "correct" certain parts of the game which drive me utterly insane. Situations like resting players because of crowded fixtures and then at the last moment (after I've rested players) a fixture gets moved due to international callups (callups which were made weeks ago and IRL the fixture would have been moved far enough in advance to plan things). I don't feel like this situation (and many others in the game I won't get into) are realistic.
Having said that I also don't want to fall into the trap of editing all my players to 190 -- what's the point of even playing the game at that point? So I have rules which I adhere to no matter what. I've curious if anyone else has editing rules? If so, what are they? Here are some of mine ...
I give myself a set amount of money at the start (it varies depending on the team and the challenge I'm up for) and then I'm not allowed any more money under any circumstances. It makes it more fun to have a little money to spend but it's not an unlimited pot where I can buy a "dream team." Practically it's also better to know exactly how much you have to work with rather than the chairman just pulling numbers out of a hat. Every season I'll edit away the chairman's limits -- I can spend whatever I want but still have to turn a profit (or carry a balance to offset any losses) to stay employed. Still have to budget the team, limit wages, and sell players to avoid getting into financial trouble but I'm in complete control rather than having arbitrary limits. It's a nice middle ground between the realism of having to turn a profit and the fun of having some cash to buy a few star players.
I edit wage budget very high (like 100M) so I can afford anyone I want. (I never actually run it up that high I just like the freedom). However I still have to pay for the players (and can't give myself any more money to do so) -- so if I go too crazy and run up the wages so high that I'm losing money then I'll be fired (and have been).
No player stat editing unless I feel the game has someone drastically wrong. If that's the case (which it was this year with a few players) then I edit them at the start and change players on all teams (not just mine).
A limited amount of "fitness" edits. I can restore a player to 100% but I only have a limited amount of times I can do it. There is no real justification for this aside from the fact that (as I mentioned before) I don't like the way the game handles fixtures at times.
No injury edits OR a limited number of injury edits.
No saved game replays of matches I lost the first time. Admittedly not an editing issue but still a good rule.
Very rarely, if a transfer issue is just illogical beyond all reason, I'll edit the problem away. Recently I had a player very unhappy and wanting a move. So I arranged a move and he ended up refusing the contract. I tried again and he still refused (even though I made it clear he had no place on my team and he himself had requested a move). At some point it just becomes IMPOSSIBLE to sell a player for some reason. IRL marginal players are sold all the time -- you might not get as much as you'd like but you can still sell them; in FM it's hard to sell anyone aside from the players you don't want to sell. I'm not saying it should always be easy but I hate the lack of back and forth negotiation in the game. Every year I'll run into situations where a player has been sold IRL for a couple of million but I can't sell him in the game for a bag of peanuts and half a can of beans.
Some people might find it pointless to have limits (if you're going to edit why not go all out?) and others might object to any editing at all. However I just want to edit out the parts of the game which annoy me. I obey my limits -- I just lost a cup final on penalties I probably could have won had I put my players up to 100% and fixed some injuries.
Overall I enjoy the game more when those frustrating nonsensical parts can be corrected.