Right, if on CL isn't playing and you have extra RPs on your bench, rotate one in.
Same with starters - you only need them in your lineup when they're actually starting.
If you have a Yahoo-type set-up (with 2 SP, 2 RP and 3 generic P slots), you should try to have pitchers who are actually playing in your open P slots. No need to have starters in there if they aren't starting. So best to have more than 2 RPs (with the extras playing in the P slot) to pick up saves (and potentially pick up wins, help your Ks and ratios, etc.).
With pitching, near the end of the season, just monitor your innings (if you're no where near the limit, you can pick up some more starters from the waiver wire, if you're over the limit, trade extra starters or use them selectively with good matchups).
Hope this helps a bit.
Mulliniks Watch: Still stuck on 1325 games 3569 AB 445 R 972 H 73 HR 435 RBI 0.272 AVG 15 SB