Ubisoft has made it official that they are ditching the always-on model for DRM. In an always-on DRM scheme, a user must remain connected to the internet to play a game, something that isn't always feasible. It also has troubles when the central servers go down or are overloaded.
Thankfully, Ubisoft has decided to move away from both this DRM model and the limited activation model. Both of these are good moves for PC gamers and hopefully other companies will follow. The limited activation model creates issues for reviewers who have to reinstall the game many times, often across multiple generations of hardware.
Whenever you want to reach any online service, multiplayer, you will have to be connected, and obviously for online games you will also need to be online to play. But if you want to enjoy Assassin's Creed III single player, you will be able to do that without being connected. And you will be able to activate the game on as many machines as you want.
Furthermore, this type of DRM defeats the purpose of gaming on a PC. Probably the best reason for gaming on a computer is the ability to upgrade. However, if you have to reinstall a game and run out of activations, the benefit of being able to upgrade is completely gone. We might as well be gaming on consoles.