Originally Posted by MattKing
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.