That's not just what I say, but what everybody I've talked to who runs for the small guys says. I can't see any drawbacks to it.
The drawbacks have been well documented here on EO. The biggest one is when you're signed on with multiple companies, it's not unusual for all of the companies that you're signed on with to be bidding on the same freight, for you, and you and the carrier end up running it for less than you would have otherwise. It happens more than you might think. More than a few people here have sat and watched it happen. Seen it myself a couple of times.
A few people have success with multiple companies, but it's just a few, and it's those who already know where freight comes from, usually.
One thing I've noticed with some people here is, they are constantly trying to reinvent the wheel using their own brand new light bulb inspired ideas that everyone has already thought of many times before. New and inventive ways of keeping warm, or keeping cool, or finding (even if you have to build it) a cheaper, better generator, yet all of those ideas have been tried before. There's a reason no one uses them. It's because they don't work, and there are other tried and true methods that have proven time and time again to work. So, people end up wasting a lot of time and money to reinvent the wheel, and end up using the tried and true, the regular wheel that someone already invented a long time ago.
It's the same with signing on with multiple companies because you're not running enough. With very few exceptions, multiple companies is the answer. For most, it's signing on with a carrier that can keep you busier, one that is either not a bottom feeder feeding on leftovers, or one that has their own customer base.
If you're taking freight that takes you to bad places, and/or you don't know the best place to go to wait for your next load, then multiple companies aren't going to help. If you are taking freight to good places, and/or know where to wait for your next load, then multiple companies aren't even necessary.
So you first have to determine why your carrier can't keep you busy. It is that your carrier is a bottom feeder, or is it where you find yourself sitting? Either way, once you've got a handle on that, you can make the adjustment. Signing on with multiple companies is more often than not treating the symptom rather than the cause. And it's a far bigger problem than finding a small engine repair facility.