Not sure about how other folks use this, but I often disable a subset of aligned images, generate a dense cloud, then enable some/disable some images, and generate another dense cloud.
"reuse depth maps" defaults to "checked" in the dialog box (advanced settings, hidden by default) (probably defaults to checked because of my "keep depth maps" setting), but if depth maps don't exist I get a "zero resolution" error, rather than (1) depth maps being created for images that don't have them, or (2) a prompt saying they don't exist.
I would prefer that when I have "keep depth maps" selected in advanced options, "reuse depth maps" does not automatically regenerate existing depth maps, but DOES generate depth maps that don't exist.
Also a quick note - Thank you Agisoft developers for being so responsive to user questions/requests/comments. It makes for a very nice user experience, and I think that it generally shows in the helpfulness and enthusiasm of the user community.