The concept of hourly comes into play here. You'd much rather win $100 in 2 hours than in 4 hours, right? Well what if you earn $90 in 2 hours instead of $100 in 4 hours? Still better to go the 2 hour route in terms of your hourly wage.
So if you have nothing better to do with your time, you should go for the full $100, but if you can spend the time you would've spent early in a tournie playing other profitable tournies or doing anything else you value, late regging is best. How late to late reg really comes down to how much time you save versus how much
equity you give up mixed in with how much you could earn doing something else.
Also granted the above are mainly considerations for a pro. I personally like to pretty much max late reg when I play MTTs on ACR just because the late reg periods are so long so I'd just as well come in for 10 big blinds once half the field as busted and a double up gets me an average stack. When I do buy in earlier I often build up a nice stack but find a way to donk it off and end up re-entering for 10bb anyways so I might as well go for the shortstacking strategy and if it doesn't work out, move onto the next one. If I had 6 hours to grind though, I'd just fire up some tournies from the start, but hen I open up the client with just a couple hours to burn, late reg is fine by me.