Ian:

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.