What is your university's policy on course reductions for service on dissertation committees?
In mathematics in Minnesota, the advisor gets a half-course reduction, and committee members no reduction.

Thus, some years ago, when I taught a crypto class and a coding class that were popular with some engineering dept grad students, and I found myself being asked to be on about 250 Master's and PhD committees within a few years, it was a task that was not literally directly compensated-for, despite consuming significant time. But I figured it was part of my service duty. I allocated an hour or two prior to the actual presentation to review the document, and the presentation itself would take an hour or two.

(My chief benefit was amusement with some of my "colleagues" who apparently thought I was grossly exaggerating, since "obviously no one would agree to being on so many committees"...)