The reason for not leaving it to 'no' for all is easy. It consumes more memory. Both static (your exe grows) and dynamic (a copy of all front panel control and indicator data is made). so removing the front panel saves memory and can speed execution time.
Setting all to 'yes' wont work because then there will not be a panel for anything the user needs to see. in other words, you need at least 1 panel to be set to 'no'. If you use other input or dialog boxes, these must be set to 'no' also.
Read chapter 28 of the G programming manual, specifically pages 28-19 and 28-20 for front panel memory issues. The whole chapter is a must read, i think, but read at least these 2 pages.
Jared