While Operating Systems are quite complicated and it is often hard to say any particular thing is causing a lag a specific user is seeing, I can say that it does seem to make a difference if you reduce the number of widgets. By default, you may have several useless widgets on secondary pages. Removing these is one less thing running. The same goes for Live Wallpapers, though I'm not sure there impact is as great as some of the widgets which may periodically do I/O bursts that slow the system down. This is all my speculation.