When should you activate your King?


It's a question which may have been asked before but...

When do you think activating your king is necessary, and indeed need. I realise there are many circumstances in Chess, but in what set of circumstances should you?


Or if queens were exchanged and the position is closed, specially the center. Seirawan wrote about this in his book and he gave his game against Timman as an example:

I think what he did was protecting b-pawn, so that he could reposition his bishop on better square without problems, and b3 square. Perhaps he could also protect c-pawn if needed. He retreated his king to e1 after position has opened, so it was only temporary activation of his king.