Quote Originally Posted by MattKing View Post

Bob Carnie fixes as well, and doesn't even try to defend it.

I've just recently started using fixer after toning or redevelopment, but for an ulterior purpose. It is a hardening fixer (the only one I use) and, per PE's suggestion, an apparently effective way of hardening without the challenges of having to mix separate hardener (which is apparently a relatively finicky process).

I of course wash after the the additional fixer.

It's really depedant on the toning process and particularly whether toning's to completion. There can be a case for re-fixing with some processes, there can even be a case for re-bleaching and fixing after some toners like dye coupler toners.

However with some toners refixing will destroy the colour / tones entirely so ideally sufficient reading / research needs to be done at the outset, or follow manufacturers instructions.

I did a lot of commercial research into toners and hardening was never an issue unless a hardening fixer was used prior to toning, then a softening bath was needed to ensure ven toning.

The OP's question is rather broad so needs a more simple answer.