Neck Dies are adjustable, but you won't likely need to between rifles. Its the brass you won't want to move from rifle to rifle, because each rifle will have slightly different headspace and the brass will expand to fit that headspace.
A body die is like a full length die but doesn't size the neck just the shoulder/body. I typically use a body die to push the shoulder back when chambering gets tight, When I do that I also trim, chamfer and anneal, then neck (collet) size. It varies a little but as a guess every 5 or 6 loadings. All the other loadings I just collet size and reload.
