1. I think a separate taper crimp die as stated does provide an additional degree of precison over a standard "does-it-all" 3 die set and if you have an empty stage on your press as must auto indexing presses do to house a taper crimp die, it makes sense to install one.
2. If you are having no functioning problems using a conventional taper crimp die that provides no final sizing such as the Hornady and RCBS, despite evidence of case bulge, there is no reason to replace with a Lee taper crimp/sizer die. Any visible bulge is cosmetic.
3. Case bulge will be more pronounced when using lead bullets, particularly hard cast as they are sized a hair larger - in the case of the .45 ACP, .452 for hard cast vs. .451 for jacketed. But again, if you are not having any functioning problems using a conventional taper crimp die, despite the visible bulge, there is no reason to switch to the Lee. The test is to drop a finished round into the barrel chamber. It should easily fall out when the barrel is turned upside down. If it sticks inside (i.e, requiring a good pull with your fingers), you may want to try the Lee.