There really isnt any reason to unless you do some rather non-standard consumer stuff. That is more than use MS Word and play a few computer games, and do such things as programming or hosting various things.
On the other hand; if you do use 64bit windows it isnt going to make any
negative difference to using various stuff.
The biggest problem is driver support might be lacking for anything which isnt a well known and highly used brand.
However, there is
no 16bit support in 64bit windows.
64bit IE cant load 32bit ActiveX stuff, which really isnt any loss. There is a 32bit version of IE buddled in with 64bit Windows, if you really want to use a version of IE with 32bit ActiveX support.
You will need to get a 64bit ready anti-virus and if you dont use the biult in windows firewall, a 64bit version of that. Personally, the biult-in windows firewall is fine.
"Okay, I'll have the truth with a side order of clarity." ~ Dr. Daniel Jackson.
"Reality has a well-known liberal bias." ~ Stephen Colbert
"One Drive, One Partition, the One True Path" ~ ars technica forums - warrens - on hhd partitioning schemes.
