You are correct in the fact that you don't "NEED" a buffer to apply waxes, but I would respectfully disagree with the rest as it really depends on what kind/type of waxes or sealants are being applied as some go on/off very easily and some do not....
As a professional detailer I can tell you that using a machine like the PC with a fine pad on a low setting is by far the best way to apply a wax or sealant. The reason being is that it spreads very very thin and evenly.
This is good cause with wax/sealants if you put it on too thick 1 it will be more difficult to remove, 2 it takes longer to dry and cure which can cause it to streak when removed, 3 it gets in all the little cracks and seems of the car. With a PC applying thin layers will avoid all this mess and you'll be saving money in products cause you'll learn to use less by spreading it thin. Less is more when applying wax/sealants.
Josh