I'm not an expert, but I have covered half the aviation law subject for my ATPL's, and if you are hour building towards your full ATPL there is a minimum 1500 hours of which "a maximum of 100 hours flight simulator time may be included" so don't do too many. If you are hour building with the aim of getting out of the "frozen ATPL and 200 hours" bracket, I suppose it is up to your bank balance.
Cheers,
Charlie Boy
[ 25 November 2001: Message edited by: Charlie Boy ]