I have no less than three reasons for having strictly avoided dongles to date.
I currently have a seven port USB hub on my main studio computer, along with four USB ports on the computer itself. And every single one of those ports (ten in total) is already occupied in the course of my normal studio operations. Similarly, I have exactly 2 USB ports on my portable computer, and when I’m using it for music purposes, both of those are filled as well. So in both cases, needing to use a dongle would require me to daisy-chain a second USB hub in the studio (yuck), or to begin carrying around a USB hub (and the power cable for same, as it would need to be a powered hub) with my mobile setup (also yuck). So that’s the first reason I dislike dongles.
Second, as other people have said, is the possibility of losing or breaking the dongle and having my studio go down as a result. At least right now, if something would happen to either of my music computers, I would have the other one to fall back on until I could get the problem system up and running again. Compare that to the scenario of having my entire music efforts controlled by the availability of a single tiny dongle, not to mention the associated software of the dongle’s maker, which would introduce a single point of vulnerability that could stop me from making music entirely, and that is something I don’t like at all.
But my final and largest concern is not so much with the dongles as it is with the associated software created by the dongle companies. I especially have a major revulsion to iLok (PACE) based upon my history with them (which I won’t burden this thread with, but you can look at my forum profile for a few details if you would like). I also used to purchase and use Steinberg’s Wavelab many years back, until their own copy protection software caused me (a legitimate, paying owner) so many problems with keeping it operational on my computers that I gave up and moved to something else. Which gives me a major level of distrust of both iLok and eLicensor on top of the general concerns about dongle solutions I’ve detailed above.