It provokes responses
There's a better, more productive motivation for following lots of others on the site. That's because doing so gives you a lot to react to. Every time you log in, the stream will be different. It's just so much easier when there are all those new tweets scrolling down in front of you. Even if you're not really in a tweeting mood you're sure to see something that catches your eye, makes you laugh, give you an "Aha!" moment. Before you know it you'll have tweeted several replies. There will also often be things that you want to retweet.
And it's really important to do this, because you'll get on the radar of many more people this way. So your follower count will grow much quicker than if you just follow others for the follow back only.
Be discerning and niche-specific
So, when going on a bit of a following binge, make sure you search only within your chosen niche. The tweets of these people will be more likely to elicit genuine and relevant responses from you. Similarly, your reactions will be specific and therefore more appealing to those in your niche.
Make sure that the tweeps you do follow are active and engage often with others. Don't be indiscriminate -- although you shouldn't be too picky, either. As with so many things, a middle of the road approach is needed.
And if you are very new to the site, you can afford to be less choosy than you are later on, when you're more established. Just make sure that the people you're following are relevant, real and active. You can always unfollow people later on. That said, you shouldn't "churn" through your following just to build your numbers. That's bad manners, and can get you suspended. It's best to unfollow only those who haven't tweeted lately, or whose content you don't find valuable.
It's a bit like blogging early on. I think when you start a blog, you should posts as often as possible, even if those posts are short. It's all about getting some stuff up there and building momentum.
It helps you gather momentum
I know that this is an emotional thing. It's not truly rational. But it's really important nonetheless. And the emotion you're getting from tweeting is a sense of connectedness. Getting those replies and retweets is fun, and it motivates you to keep going.
It's sort of like going to a social event. While there's something to be said for just sitting there for a little while and taking things in, you don't want to do this too long. And you don't want to be too snobby either. It's a good idea to mingle. If you meet lots of people and there are sure to be a few you really like and strike up ongoing friendships with.