This is being discussed as an aside in a different thread. I thought the topic deserved it's own thread.
I use a trumpet/cornet stand in my practice room. I usually play for about ten minutes at a time. Although, I might do this 3-5 times spread across the day. It's so easy to just pick up the horn and start playing.
If I keep the horn in the case, I always zip I shut. My worst fear is that my wife or son will pickup the unzipped case and the horn will spill out. It's kind of a hassle to unzip the case to get the horn out a bunch of times throughout the day.
If I were playing out somewhere, I might be more inclined to use the case. However, I also play keyboard. Sometimes I might need to jump off the keys to play a part on the trumpet and then back to keys. A stand seems helpful here also.