@MattKing I searched the archives a while ago and found a post where even PE said he had no idea why would someone use a bleach starter. He did not know what it was for. I am too lazy to do it again, but I wasn't able to find any sensible explanation for its existence, so it's pretty close to the definition of nonsense.
Hi, if you look up Kodak CIS-61, pH and specific gravity specs for Kodak chemicals, it shows that there are different pH aim values for the C-41 "tank solution" bleach vs the bleach replenisher.
So if you buy your bleach in the form of replenisher, and try to use it directly, it's most likely not gonna be at the aim value for pH. Now, because of the broad pH tolerances (per CIS-61) it's probably gonna be in a usable range. (Maybe not, though, if tolerances pile up the wrong way.)
Anyway, it seems pretty obvious to me that the main thing with a C-41 bleach starter is to raise the pH of the replenisher, getting it near center of the aim point. So on an amateur basis people probably find that it seems to work fine without a starter. But someone working on a more serious basis would probably prefer to get closer to the pH aim spec.
To others: Sorry about this diversion away from Xtol.