Yes, a projector is much more portable than a 100" flat panel and that's great. But, as you say, you've got to either have two or more screens or move one to different locations and install it.
If you're moving from one neighborhood or city to another, which people do more and more nowadays, moving the screen and installing in a new abode is a one-time task. If you're moving a great distance, good luck preventing damage to the huge, expensive panel. But it's all doable.
Because a 100" panel will likely still be well under 100 lbs, the major problem will be getting the thing around corners, down or up stairs, etc. For example, in our home's case, I'd likely have to remove some drywall to get the thing into position and then re-install drywall, seam and paint it. My wife and I don't relish the thought, but for a one-shot deal we'd do it. OTOH, if large panels are made at least somewhat flexible, that would be a horse of a different color.
Also, because a panel's image will likely be brighter and more view-able in pretty bright light, we might install it upstairs rather than in the basement and use it as an everyday, all-in-one replacement for our 70". Then no "remodeling" necessary. In this case, to get the immersive effect of a large apparent image for movies, the chairs would have to be dragged closer to the screen. In our case, for a 100" wide panel, our two sets of eyes would want to be about 80 inches from the center-point of the panel. Most people would sit farther back than this even for a 65" TV, so unless the chairs/sofa can be easily slid around, a permanent room arrangement for that viewing distance is going to look a bit weird and cramped.
(Our present viewing distance of 96" from our 119"-diagonal Dalite HP 2.8-gain pull-down screen also looks a bit cramped, furniture-wise, but the viewing experience is fantastic. Whenever guests first see our HT, usually they sit down before anything's projected onto the screen. Almost invariably, as soon as they sit down they say something like "this is too close for me". But shortly after a movie starts they also invariably say "this is just like being in the theater! Fantastic!".)