I do 30 PSI just to ensure I have a good seal. As stated, you could simply pop the tops off and auto siphon with out using CO2 (other then a little to seal the keg force carb etc).
That said, I have a 5# and 2 20# tanks; I haven't even emptied/refilled a 20# yet, and for $14 a fill, I don't mind using it to ensure I have good beer. I just like having a closed system at this stage at the cost of a little CO2, rather then opening it up to possible contaminants (I'm fairly anal with sanatization in all steps of my brewing processes, even in my transfer method- Why risk it when this is just as easy and more beneficial in my mind?) Happy brewing!