I used to often quote the "speedwork is easier in a group" line.
Now I think that's bullspit.
Chances are that in your average club you're doing it with a bunch of completely different abilities, and have no idea of the correct rep pace, length or recovery, meaning that you don't get a quality work out, and instead are trying to compete with people in training...never a good idea.
I much prefer doing a speed session on my own, knowing I'm doing it to my own designated pace, know the amount of reps...know the recoveries etc.
Before I used to fool myself that a miscellaneous club session of "run fast to that lampost, jog back, then run fast to the next lampost" was a good workout!