Closed-back headphones are ideal for tracking, as they provide the most isolation from outside sound getting in and headphone sound getting out (aka bleed) which can mainly be a problem when doing vocals since you and the headphones stand very close to the mic when singing...so the bleed from semi-open or poor fitting headphones could get into the mic and you end up with your vocal track plus some ambient, backing track signal mixed in.
It's not always a problem, but ideally you don't want anything there but your vocals.
Semi-open headphones allow a little of the outside sound to come in, they are more natural sounding and are preferred if you want to do some basic mixing/listening/editing with them, however, you CAN also use them for tracking where "bleed" would not be much of an issue and you don't want/need solid isolation from the outside sounds.
I use my semi-open all the time for tracking guitars, keys, etc...there are no mics near the headphones, so bleed is not an issue and I like to be able to hear some of the "room sound", especially when playing guitars, though most times I don't pay too much attention which type of headphone I grab for tracking, unless I'm doing vocals, and then I go for the closed-back...though as I said, the semi-open usually sound better than comparable closed-back models...IMHO.