It's important to note that
1. Yes, the clip effect will only be heard for the length of the clip, so reverbs and delays may need some extra clip length for their tails, but
2. The clip effect (unless VST3) is actually using CPU power the whole time, not just when you're playing the clip. So in that sense it's the same as a track effect.
Just pointing it out in case you were hoping to conserve CPU power.