I can't see any advantage to checking in early generally, and definitely don't see the advantage of checking in days early. Most of our reservations are cancelable, and something could always come up that changes our plans.
In cases where someone books through a third party (Expedia, etc), checking in days early could really bite you. You would have not only the hotel's policies to deal with, but also the travel site's policies. Lots of folks have gotten stuck using third parties, so I use them only to research fares and hotel rates -- then I book directly.
I get some benefits from Hilton Honors, but those have nothing to do with early checkin.