Huh. I just learned something really interesting here.
To test this out, I split a vocal clip, added GuitarRig to the clip, and used Quad Delay on the preset called Forever. Sure enough, the delay cut off abruptly as soon as the next clip started.
Since I don't generally use clip-based effects, this was very enlightening and I can see ways to use this effectively. And, of course, why this would not always be the right solution.
Thanks Craig and FBB.