Not ENTIRELY true... the advantage to checking in early is that, in the unlikely event that the flight is overbooked and nobody volunteers to give up a seat, they involuntarily bump people based on whomever checked in last. Thus, if you can't take a bump for any reason (like when travelling to Disney with kids

), check in early!
If you don't have your printer hooked up, check in anyway. You can go back and print the boarding passes any time -- just go back to online checkin and it'll say "already checked in" and give you the option to reprint the boarding passes.