I use my ST-E2 alot. I always have it in my bag as I hate on camera flash, so if I need to use a flash I use the ST-E2. (When the space is too big or too sunlit for the IR to work I then use a off camera cord.)
I don’t always shoot in eTTL but when I do I use the ST-E2. Its nice to have choices.
only just learn the potential of ST-E2 recently. I have always use manual and trigger with PW.
I use PW’s when I want to shoot manual, which is the rare occasions I do a portrait. The ST-E2 is a great tool to have though.