i guess it depends what you want out of running, i am a member of a club and may do a few sessions training with them through the winter, however as an ultra runner (there are a couple of others in the club)we often need support crews and i find that the best place to get support is from within the club, and for my part i get almost as much pleasure from supporting somebody on an ultra as running one oneself.
Although i am an infrequent runner with them when i do show up there is always a welcome and lots of catching up to do on one anothers exploits be it a 5k or 100+ miles it matters not, and they are a great bunch of folk.
The welcome they give to newcomers is superb and nobody is ever left to fall off the back, and it is not uncommon for the faster runners to run back on the group and run at the back and give support and encouragement to the slower folk.
In short i often wish i had the time to train more often and be more involved with my club, but when you are covering 100+ miles a week and working full time then it is a juggling act as to where when and how.
I always wear my club vest as i am proud to be a member of the club even though i am just on the sidelines most of the year.