You're on a roadtrip and you have to pee, but you're not exactly in a convenient place to stop. It's easy to think, "I'll just wait for the next rest stop." But you'd better not if the next bathroom is far away.
Holding urine is bad for you, if you're holding it for an extended amount of time. Frequently holding it in may have some negative long-term effects like urinary retention and an increased risk of infection.
Adult bladders can hold up to about two full cups of urine before the brain is signaled that the body needs to relieve itself. When you hold it beyond capacity, the bladder's cylindrical sphincters close tightly to keep things sealed.
Learn more about holding in your pee and about the very rare instance of an exploding bladder -- don't worry, it really is rare -- You might not take that nearby office bathroom for granted again.