What if your leased to three different co's. Co. one calls we have a load for $.85 you say ok. All three Co's have bid on same load. Co #2 bids $.65. Co #1 calls and say's we lost it. Co #2 say's yes or no? Co #3 bids $.55 and bumps #2 out. Where do you stand then?.
And say you took it (now at $0.55, unlikely, but just pretend for a moment), and you now need to tell Co#1 and Co#2 where you're headed, or call them when you're empty and tell them where you are... and depending on the situation, it won't always be difficult for them to know what you did, and they might ask how much you got for the load.. it just creates bad karma all around. (Oh, you mean it was YOU that undercut YOURSELF and bumped us out of the picture?)
Which is likely to happen with the companies that will allow this sort of arrangement. Other than customer accounts, most companies are getting their freight from the same sources. Most of the time I don't think the truck has a better chance of getting loaded in those situations, just a better chance of the load paying less than it should because of false competition.
Most carriers are hooked up with a certain load board.. which offer all different packages to carriers, depending on which services they subscribe to.. and it costs money for these carriers to post an available truck... if you are really 'not' available (to them at least), they're going to think twice about putting out the money to post 'your' truck. The carriers also have their own reputation amongst the other carriers to think about, (and it doesn't help reputation when one posts a truck as available in a certain area, and the truck declines), which is more important to them than whether you stay loaded and happy.
I have worked for two companies at the same time before ane neither one would call me for loads that were being posted in my area. So, maybe if I had been leased on with a third carrier, the third carrier might have called me on one of those loads. You can't always trust one carrrier to bid on loads for you and look out for your best interests.
This is just a stinky business, I'm sorry, but it is. So you're hooked up with however many carriers that will take you, but it still doesn't guarantee that you're going to be the one getting that load that comes up just where you happen to be located.. the carriers are going to go with the OOs they can count on first.. and even if you're equal status with someone else, there's always that pesky 'FIFO'/sharing-the-wealth thing to consider.
And say you have a pallet on your truck for one carrier, and a second carrier has a rush on a single pallet which you determine you can also run along the way.. but you know that the first carrier would terminate your contract if you were to put another piece of freight on with the freight they've promised their customer will be exclusive in your truck. Money talks, so you decide that carrier#1 doesn't need to know.. but wouldn't you know it, you get held up at the consignee for the load which carrier#1 doesn't know about, and now you're going to be late with the carrier#1's delivery.. or say you hit a deer with both skids on the truck (which carrier#1 still doesn't know about skid#2) and it spins you into another vehicle causing personal injury... whose insurance is going to cover you when the battle gets ugly...
IMHO it's best to find a carrier you can trust to treat you as fairly as possible (it's never possible to treat
you (you, as in the reader, and meaning nobody in particular) totally fairly, considering they have the same obligation to numerous others) and commit to them, or get your own authority, or go with a carrier who mostly deals with their own customers rather than other carriers and brokers, or go with a carrier who will only charge you a small amount to use their authority to broker some of your own freight when you need to.