Orrr, from my POV - I can go to bed at midnight, have a quickie and be fast asleep by 12:20... or I can go to bed at midnight and argue for 45 minutes about how I'm really just too tired tonight, babe, can I please just go to sleep and we'll try again tomorrow? And then by the time he gives up, I feel like a cow for dragging it out for so long when I could have just told him, 'Okay, but don't expect fireworks tonight' and had it over with in 15 minutes!
Again, that's just us :) DH has a habit of treating sex like a sleeping pill anyway so there are nights we DTD even when neither of us is particularly fussed about it - it just helps us both sleep better.