Not nessesaraly. The engine may have to be put under a load in order to torque the crankshaft.

The seal can be done without yanking the crank. It takes some doing, but with the main cap removed. The technique involves fishing the seal out on end and inserting the new seal from the other side, using the new seal as a "ram" to push the old one out.

Imagine that! Some hot shot engine bulider installing a leaking rear main seal. But wtf would expect from a typical mechanic?

And me, certainly not a hot shot engine builder still having a bone dry rear main seal after 18 years and 130k miles. (Maybe I'll set it up on stands, weasel underneath with the camera, and take a picture of the amount of grime after 2 decades of abusive useage.)