I think like other people have said the main reason to pre-order is to make sure you get the memory option, color and model you want without having to be at the mercy of whatever is in stock at a physical location.
Also when you pre-order you get your device slightly early, don't have to leave your home, don't have to deal with lines (if there is one) and you get to relax instead of dealing with pushy store reps, parking issues at retail locations, computer systems going down, etc.
I will still pre-order whenever it comes to a device I want, I don't really care about getting it 7 days early or 1 day early because skipping the lines and getting exactly what I want is 100% better. I think pre-orders are far more important when it comes to iPhones because of massive shipping delays but all other manufacturers seem to have enough inventory for their launch day.