I joined Wrekin Road Runners in July 2013, since then I've become a better runner...
It's sociable
When I moved to Telford I worked, and still work, in Wolverhampton. The only people I knew were my colleagues. Lovely bunch but you can get too much of them. Joining Wrekin Road Runners has introduced us to loads of different folk and they also enjoy the odd social occasion too.
It's safe
It's understandable that a lot of runners don't like doing it by themselves, especially as the winter nights draw in and it's dark at like 3.00pm. This leads us on to...
It's motivational
If it is dark and cold you are less likely to go out on your own because it's much more cosy in your lovely warm house. With the appeal of catching up with others and not wanting to miss out on that 10 miler or hill repeat session, chances are you will be out hitting the tarmac in no time...
You will get faster or fitter (probably both)
This may happen anyway but in a group you are probably going to go out more regularly and by running with others who are slightly faster than you or can run slightly further than you, it follows that you push yourself harder and see faster improvements. I first started out with a half marathon time of around 1hr 50m, quite pleased with that time. My friend challenged us to run the next one in Bristol in under 1 hr 40, I thought this would be tough but after training with the club for only about 8 weeks it felt like a breeze, coming in at 1hr 47min or so. Six months later I was in full marathon training and ran Stafford Half in the run up to it. 1 hour 30 min (and 20s) and a new PB! Couldn't believe how far I'd come in such a short period of time.
The competition is healthy
When you get in to it, competing with others is great. It might be in a race, it might just be on a club training run but competing with others is a sure way to improve in any activity. It might just be that last 100m dash with a complete stranger but the feeling of being first over the line is fantastic (even if there were 200 other people in front of you!)
You Learn
When you first start running you know very little about anything: Kit, nutrition, training plans, pacing etc. Good thing is you don't need to know much to get started. You just run. And that's good. Then as you become more regular you talk to people about all of these things and you learn the right and wrong ways to do things (just watch who gets injured most regularly...), which kit works best for you, which gels make you feel sick and which ones make you feel like you could take on the world. You learn how fast you should run in training and how fast to run in a race. You learn that if you run a race every week, you will not only be skint but you will also not get much faster because your body can't recover in time....well you might do.