What is the functional difference between a fixed plate pulley and a swing plate pulley?

Why would one prefer one over the other? Is one better for hauling and one better for rescue?

My understanding is that fixed plate pulleys are generally not as efficient as swing plate pulleys, although this has to do more with the sheaves that are typically associated with each type of pulley (i.e. I’ve never seen fixed with a sealed ball bearing sheave, aside from maybe high end zipline or some heavy industrial pulley). Just my two cents.

Higher Education (p. 246) outlines a few reasons why one might prefer one or another.

1. fixed design tends to be stronger

2. typical fixed design necessitates an oval biner

3. typical fixed design makes it easier to position the pulley within a biner

4. some swing pulleys have the plates set close enough together for prusik-minding

Thanks all!

Eli W wrote: 2. typical fixed design necessitates an oval biner

This one jumped out to me of all the reasons. I will have ovals with me if, for example, I have a selection of nuts on my rack because I usually have an oval biner for the large and mediums and one oval for the rest. But if I didn't have those for whatever reason, I typically won't have on oval on my person, so the swing plate would then make sense. I have a fixed so I'll pick up a swing to cover both scenarios or to let someone borrow.