I don't quite follow.
If I mark a profile field as required, and uncheck "require valid profile for registration", then the user:
1) Registers on the site
2) Comes to login, and is forced to fill out their profile before continuing
If I mark a profile field as required, and check "require valid profile for registration", then the user simply registers and fills out their profile all in one fell swoop.
The only difference is whether or not the user has to complete their registration in one step, or two steps. I prefer one step :-)
Regardless, it would probably be helpful if somewhere on the profile manager we had a bit of clarifying text that explained that you have to check "require valid profile for registration" in order to get profile fields (required or not) to show up on the registration page.
Perhaps the best solution would be to only have required profile fields (not all profile fields) show up on the registration page? For instance, in my case, the only additional profile field I need is "ConstituentID". But it's showing them a place to fill in every profile field.
-Josh