You absolutely need the iLok in at all times. I use a USB hub with my MacBook Pro, and occasionally the computer won't be able to find the iLok (I also have 2 MIDI devices and a USB mouse plugged into it, possible conflicts), and it'll make me save my session and close Pro Tools. Now I make sure the iLok goes directly into one of the MacBook's USB ports. So it must periodically check. If it didn't, you could theoretically start Pro Tools on any number of computers you wanted to with one license just to get them started.