Situation came up for my wife's commuting this week.

Based on what I've read here, you give yourself one primary commuting flight and one backup. If you can't get on the first one, you call the crew desk and they'll PS you on the 2nd. No harm, no foul. Don't use it often since it'll draw attention to yourself, but it's there if you need it. Or maybe it was the two flights then call the crew desk.

However, wife was told by a captain on a previous trip that if the crew desk has reserve coverage in the domicile you're commuting to, that they won't necessarily give you the PS - they can pull the trip from you saving the PS revenue loss and give it to a reserve, taking the $ out of your month.

We didn't find anything in the contract either way spelling this out (granted, we didn't search for everything outside of commute policy of 'you don't show up - you don't get paid).

In the previous threads I've read here about 'should I bid for this domicile or that since I'm commuting anyway?' nobody has commented about the crew desk possibly yanking your line trip if they have reserve coverage where you're going.