This idiom is used to warn someone not to stress about future events that may or may not occur. Too frequently, when we develop what we believe to be a decent idea, the office doomsayers list all of the potential problems that could arise. They take great pleasure in outlining all sorts of fictitious issues that will prevent the project from succeeding. If you tell your critics in this situation that you will cross the bridge when you get there, what you really mean is that you will deal with the various issues as they come up. Right now, you're not going to worry about them unnecessarily.

What if we run out of funding? We'll cross the bridge when we come to it.

Mohan seemed unconcerned. He said that he would cross the bridge when he came to it.