Well blowdrying is a direct blast of heat against your hairshaft, and most people blow with comb attachments as well as brushes, pulling at the hair while wet, and wet is typically a more vulnerable stage. Sitting under the dryer is more like gently heating the hair to help it dry from a distance, products can work better as it works its magic over the 30 min plus that you sit there as opposed to wham bam blow my hair out. Its like the difference between being in a walk-in freezer as opposed to just being in a room with great AC...both cool you down, but one is obviously more drastic than the other.