I'll comment on the two overlapping issues in your question.
First...related to long term injury. The following is my approach.
Let's say I have a player like Milton Bradley. He has about a 40 game long term injury risk. He had about 400 Plate App. Since he has long term injury risk, the game system allows him to play into a much higher PA use number before he is worn out. If I rest him to lower his PA use, I get less PA's out of him now. As his PA use declines, he approaches 110, etc. However if he gets injured, he'll miss alot of games (during which his PA use will decline). Then, with the games lost due to his injury, combined with electively rested games, I may not be able to get him up to his actual plate appearances for the total season. So I don't rest Bradley. He starts every game he is not injured. If injured, his PA use declines toward 110. IF he manages to use up his seasonal PA's prior to using up his injury games, he will become worn out, and not be useful for the rest of the season...and I send him to the farm for the rest of the season. He will be ok for any post-season games, but he may still be at risk for a long term injury then. If I end up using up his seasonal PA's, I figure I got my money's worth. I have backups to finish out the season. I hope he gets hurt, however, and I can use up his long term injury games in the first half to 3/4 of the season. My experience in PB, is that very few of my players ever use up their injured games risk.

If I rest the player at all, for a full time player like Bradley, I may have trouble getting my full money's worth of PA's out of him, so I let them play full time from the start of the season, and hope they get injured to get their rest time in.

If your player has no long term injury risk, the game institutes a gradual PA restriction such that at about game 145 of the season, no players are used above 110 PA use. It looks like about game 35, the system uses a PA use of about 134 to call a player overused (and restricts his use). Over the next 35 games, the PA use limit will decline further...to perhaps 128...etc, eventually reaching 110 by about game 145.
If your player has long term injury risk, or is a part-time player, the game system does not enforce the PA limit as closely.
Hope this helps.