Not being able to breathe sucks. Not being able to breath because there is a 200 lb person on top of you putting all his weight into your stomach and chest is even worse. Knowing this guy is doing everything in his power to find a submission hold on you while you are struggling to get a limb free to defend yourself is just the icing on the cake.
Life may not give you many situations where you are in a panic situation. Thankfully real life emergencies are few and far between, but they do happen and it is good to know how to handle yourself when they do.
Few things prepare you for panic situations like the one described above. You may not think it translates to real life situations, but Jiu Jitsu prepares you to think in the middle of bad situations. Your task in that situation is to think of the optimum maneuver to get yourself out of the jam. Do you freak out? Do you do the first thing that comes to mind despite knowing the outcome? Or do you use your head to calmly and with forethought perform a maneuver that will put you in a better position.
Keeping your cool in extreme situations is a skill that will translate to everything you do in life for the rest of your life.