I had some issues lately, but it was mostly on steam's end (I think). I'd get disconnected from a game during match start and try to close and restart it only to find that steam was having issues at the moment and I couldn't connect to them, meaning I couldn't log into the game. Although I don't think my leave count actually went up for any of that, despite me actually missing for an entire match once. On the other hand, I have had to leave matches to take care of CA/Mod business and those totally counted.
Originally the leave count was heavily pushed for by the community. There was a large trend for players to join games and just jump ship mid-match when things weren't going well for them. This happened just a crazy amount of the time. Instead of other penalties, the leave count was put in place so players would be aware if someone on their ship wasn't going to stick around, and acted as an incentive to keep people playing through the match. Nowadays we have a lot less people leaving midmatch, and the leave count is generally just annoying for the individual, as others are far less likely to care about someone else's leave count.
Although whether the leave count actually reduced the amount of players leaving midmatch is hard to tell. For instance we had the quick join, and it was believed that was responsible for players joining midmatch as a second gunner or pilot. Yet even with it mostly removed, this is still happening (although it probably is happening a lot less).
I would say that the leave count doesn't actually provide much of a benefit. It's still nice to have around, as occasionally you'll run into that player with 80 matches and 64 leaves. Perhaps having the leave count reduce by 1 every 10 matches or so? Or maybe just over time, each weekend they'll take off 2 or so?