Kegging question

Hello all. Just a quick kegging question here. I am about to keg for the first time. My question is this. I transfer beer into keg and then apply co2 to whatever level I decide. It may be dialed in at 30PSI with a good shake or I may decide to go to 10PSI and let it sit for while. Anyways let's say for discussion reasons that I choose to dial in at 30PSI. So I let it sit for a day connected. and I have it at the temperature I choose. At this point can I disconnect the co2 tank and keep the keg in the cooler and put the co2 tank somewhere else until I am ready to pour? I know once I am ready to pour I will need to reconnect the co2 tank. My thought process says that since the keg has already been filled with co2 and sealed properly that what co2 is in the keg will have no where to go, so it should stay carbonated. When it is time to pour it should need another boost of co2 to get it flowing again. Am I correct here or am I off base? My friend says he does it all the time and the beer never goes flat.

Once the beer is carbonated you can disconnect but you can't just fill it to 30psi and disconnect. If you force carb to 30 and do the rock and shake method. then the next day pull a pint and it's carbed the way you like it then you should be good to disconnect.