That's good to know. I'm still barely into the game, so could you give an estimate of how long the game lasts in single-player? Also, what, exactly, do I get from full synchronization? Are the forced actions worth the prize or should I just ignore them and play how I want?
I called it useless for a reason.

It does nothing. Like someone mentioned, and its a fair enough point, Ezio killed these men a certain way. For Desmond to truly sync with Ezio he has to do everything exactly how Ezio did it.
It yields no benefits though...making it completely useless and utterly annoying.
If you get sidetracked and purchase buildings, manage your assassins, get Romulus keys and assassinate Templar agents you're looking at easily 15+ hours. Thats also considering you use the tunnel system as a transport and not run through the country side.