According to user's manual., you rotate spare tire on the rear passenger side. If you do that every time, down to the end, will you get more tire wear on driver's side? If so, does that cause any problem?
Personally, I wouldn't bother to rotate the spare. Never have, just have always kept it as a dedicated spare.
On a FWD with non-IRS, you could almost get away with never rotating tires, just replacing the front two as needed over time. The front tires do all the work - weight, turn, drive - while the rear tires just roll, doing little work compared to the front two.
With rotation, you end up spending on 4 new tires at a time vs. just the front two.
With FWD and IRS, the rears get a work out, but still no where near as much as the fronts.
With AWD, all tires are "working" (fronts still more than rear), so rotation of all 4 tires makes sense.
I followed the manual and rotated my spare into the mix. My idea is that once I rotate the spare to the right rear, then to right front, then back to the spare location, the next place I'll put it is on the left rear, then left front, then back to the spare location.
Then I'll start over like the manual states.
The only reason I can see for keeping the spare rotated only on the right side is that that side of the vehicle tends to be the primary drive, and hence wear side of the vehicle.
Since I don't know if that's true or not, I'm planning to work it into the left side of the vehicle eventually.
I'd be interested to hear more about what others think though.