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.
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?