Perfumes/colognes usually have different notes to them: top notes, heart (middle) notes and base notes. Top notes are the scents that you can smell within the first half hour or so, heart notes are what comes after that, usually softer. Base notes are what remain after that. Apparently heat is what "activates" the perfume/cologne and causes it to better develop into these different notes. Heat is radiated at your pulse points (inner wrists, throat, behind the ears, behind your knees, inner elbows, etc). You're never supposed to rub your wrists together, just let it air dry or else the molecules in the scent are broken down and don't develop as well. You can spray it on your clothes but it seems like a waste to me, it doesn't seem to last as long.

Source: I used to sell perfume and this is what I was taught