The most annoying point for a LoF error to occur is when you are entering a downed scout. Had a sebellian officer shoot through 2 walls and kill my major (he was my original sg.) standing far away and diagonal from the entrance. I spent ~200 TUs trying to find an angle to shoot back and I'd either hit 1 wall or the other on that first corridor.
I don't mind that every alien is an elite sniper, or can take 120 damage and heal back 60 the next turn. You can plan around those and use tactics to severely minimize the risks. It is frustrating as a player when the ai gets to take impossible shots (the officer fired 2 and both hit since my major was in Jackal armor) that negate carefully thought out tactical positioning though.
Note: I was using Community Edition mod though, so it's possible something in there messed with the LoF code and the base game isn't to blame at all. I never had an issue with LoF in vanilla, but if other people have it might just be a bug that occurs every once in a while.