Unless your band is performing at a very high-level venue, you are usually lucky to get a brief line check – you jump on stage, plug into the sound system for the first time at the start of your set, and the sound person give you a thumbs-up that he has a signal from you – before you start to play, let alone a full sound check.
So if you don’t get that thumbs-up, your band starts losing time from your set while you and the engineer try to figure out the problem in your signal chain! While you can’t always prevent an issue caused by sudden gear failure, you can avoid issues caused by misconnections…