You'll only have one
reserved time to ride those rides. I don't get the whole thing about only being able to ride a ride once. In the "old days", people would pull a FP and then immediately get in the standby line. They'd ride once on standby and then wait for their FP time. If they absolutely positively had to ride a third time, they could pull another FP
if FPs were still available, which wasn't always the case. During Thanksgiving week in particular, it wasn't unusual to have FPs gone for popular rides early in the day, meaning that once you had one standby ride and one FP ride finished, you couldn't pull another FP for later. It's not like the "old" system (once they started requiring you return during the window) allowed people to ride a gazillion times with no waiting.
If you want to ride something multiple times, you get to the park early and ride standby, just like before FP+ reared its ugly head. Then you also ride your FP+ time, which means you've got two rides. And if you notice that the standby line is relatively short later in the day, then you can ride it again, just like you would have in "old FP" days if all the FPs were gone. You make it sound like once you've reserved your FP+ Disney will physically bar you from riding at any other time.
And even with "old" FP, you needed to make sure you didn't miss your times. Otherwise, you'd be stuck in the standby lines (or have zero rides on those attractions).