The speed difference is apparent if you are short on memory space (calls to IE routines), have a slower machine, and seems to be increased if you had access restrictions in place (eg. ZoneAlarm limiting access to 'Net for Poser) as Poser code likes to retry things that don't work.

But the original reason for removing it was that P5 when released was about as stable as a drunk walking the plank off a 19th century sailing galley on the high seas in a gale storm.  And with the Copy Protection code originally present, any sign of Poser throwing a wobbly could cause Interlok to crash your OS in addition to Poser, hiding all traces of the crash cause in the process.  So adding underlying IE code developed by M$ to the mix was not exactly helping!  There was a real need back then.  But it can't hurt, even now, as less code loaded should mean reduced risk.