You must urgently go to the toilet, but you are waiting for the last moment because you are typing a new message, warming your food, driving, etc. How bad is it to keep your urine? How it reflects to your organism? On basic terms it is not dangerous, but if you do it too often then it gets. A grown up person can keep half liter of liquid until you get to the moment when you must go to the toilet. But if you keep holding up your urine constantly , it can come to a state which is called urine holding , when you are not in the possibility to empty your urinary bladder completely.
Then the walls of your urinary bladder are weaken which can be a call for numerous bacteria. That is how you get a urinary infection or a common inflammation. In rare cases your urinary bladder can rupture, but then she is very damaged.
Take a look at this very educational and interesting video.