I use the lee crimp die in 9mm,.40and .45 auto. On .45 the die does not do much as long as I do not over bell the case. When I used to load range pick up
in .40 the FCD. die would sometimes size the brass if it had the glock belly on it
by screwing down the sizing die a little,watching case length and flare I have pretty much eliminated the post sizing and I have also accumulated a working supply of .40 brass that does not have a bulge in the first place. In 9mm it is pretty much the same story, I trim my cases,size properly, don't over flare and I separate head stamps and unless I use range pick up or military brass I won't get any post sizing but I scrounge brass like crazy and it is not uncommon for me to come home with a fair amount of once fired cases so I still use the FCD. I have never gotten any reduction in bullet diameter that I can measure. I think that the dies are tools that have a purpose in some circumstances just watch how you use them and you may find you like them.