Why is elevation important for fractured ankles after surgery? Isn't it enough to keep leg straight and flat?

I recently had an ankle operation and elevation was suggested.I elevated for more than a week; the exercise was painful especially when I had to remove the leg from the elevated position down towards the floor. I decided to remove one pillow and on occasion just put the leg straight and flat whilst in bed. This practice significantly reduced the painful experience. Are there any implications when not elevating but keeping the weight off the leg in the manner I've described? Your kind advice and thoughts will be highly appreciated.