The media is full of juicy contract dispute stories. Cases such as Chuck D having his royalties syphoned off catch our eye because they're so emotionally charge. (Here's a running list of outstanding court cases artists have filed against their labels.) Being quite skepitcal of the value major labels offer for artists, I know I've contributed to this phenomenon as well.
But we shouldn't dismiss contracts altogether. In fact most of the time I'd say they're largely benficial for the simple fact that they set expectations.
When people aren't sure exactly what you want/offer, they fill in the gaps with their best guesses.
Say you offer to help a young band start their merch table by going through the ordering process and having it ready for their next show. You were smart and got paid up front, right?. Great. So you go to their show, drop the merch off and leave to scamper on your merry way. As you head for the door, the other guitarist grabs you by the shoulder, "Whoa dude, where are you going? You can't leave the table unattended!"
After a short bout of confusion, you realize the other band expects you to run their merch booth from now on. Apparently the phrase "help out with merch" had very different meanings between both parties and now everyone is pissed off.
Had there been a contract, everyone would be happy now.
Contracts are how you make sure everyone gets what they wanted. Or at least it makes sure no one is angry enough to stab you.
When money or (extensive) service changes hands, it's important that both parties understand exactly what they're getting. Sometimes it's ok to just take people at their word, especially for small things like offering to help pass out fliers. But for any substantial deal, it's wise to get at least some writing to add clarity to everyone's desires.
If you get a contract for a big deal like a signing or tour, and you don't understand even one phrase, get a lawyer. Paying a hundred bucks is a whole lot cheaper than losing a lifetime of revenue by giving up your masters. Remember, contracts are about clearly setting expectations. If you don't understand what's being expected of you, don't sign it.