Compacting Registry

Hello,
I've never really given this much thought but now I am curious. I used to use system mechanic, until I decided there was better and less resource hogging freeware. Any ways, I uninstalled it way, way back and even though it was uninstalled it still to this day compacts the registry. Is this a good thing? Or can I turn it off through msconig to speedup my boot time?
Guess all I really want to know is how important is it to have yor registry compacted constantly? or at all? I am not sure but it seems to me it may slow things down while uncompacting a registry key when being used?
Thanks guys for your opinion
Jaza