I wanted something that I could position in the center of the FOV. I try to do everything directly under the lid camera whenever possible, because of alignment error. I just thought it would be very useful to be able to lift a piece out and put it back in exactly the same place (or repeat a job on another pre-cut item).
I once cut a set of runes and noticed it would be nice to be able to engrave the runes on a piece of 1/4" material, then remove them to do some clean-up or finish sanding (I wasn’t using masking at the time) and then put them back to cut them out. It is a lot easier to do surface finishing on a single plank than to do it on 25 small pieces.
I’ve never had any issue with the crumb tray shifting on me. Most of my parts so far have been small and the crumb tray seems to sit fairly solidly in the bed. I’ve since tried to move the crumbtray with my hands and it doesn’t budge. It is heavy and sits rock solid in its indents. Not even a wiggle.