In my opinion, the flap pocket is quite a bit more practical than the standard patch pocket. If you put anything in the standard patch pocket, the moment you bend over to pick something up, it will come spilling out. This obviously doesn't happen with the patch pocket, if the button is buttoned. That being said, I think a lot of us today end up understanding the pockets on our chest more as an aesthetic compliment, not so much as functional pockets. I think many of us end up choosing one pocket or the other based primarily on aesthetic preference.
It also goes without saying, but I will say it anyway, the standard patch pocket is a classic, can be used, and some men prefer it for both aesthetic and functional reasons. Some days I like the standard patch pocket more than the flap pocket. So many things all have their own unique virtues. Everything has it's own time and place.
Some days I use the pocket on my chest, some days I don't. I used to use it less, but once I began to think more deeply about the natural value in using all of the functional aspects of our clothing as intended [or close to], rather than keeping it as a non-functional aesthetic element, I began to use the flap pocket more regularly. Consistent readers may remember that I have also written about the use of the front pockets on sport coats as well.
Different men will use their flap pocket for different items. What they hold in their flap pocket will obviously depend on what they do for a living, how they live their life, what things they always need or would like on hand. Maybe the contents even says something important about them. In my pocket what can be found is either my cell phone or my kippah [yarmulke]. Sometimes I will have both in there, but both can be a bit bulky, so I generally have either one, or the other. My kippah is thin, so keeping it in the pocket on my chest is almost entirely unnoticeable. My phone is also quite small and keeping on my chest is also not so cumbersome and the button flap truly comes in use so that I don't need to worry about my phone falling out and breaking on the floor if I bend down to pick something up.
I don't use my pocket everyday. Some days I use it more than others and some days for one reason or another I just end up not using it. In addition to there being something oddly satisfying about using the functional elements of something for functional purposes, there is also something deeper about not simply keeping functional aspects around just for show. Usually if that happens long enough, those functional aspects often end up disappearing altogether. There is something about use as naturally intended. It seems like there is something satisfying and purposeful about it.