I increased my ratio as I live in a hilly area and the descents are better on a bigger ratio.
I've been going out with a mate who has gears and loves the hillier hills. I tried freewheel as I felt guilty holding him up on some the delightful descents we have that are literally miles and miles long.
If your knees are fucked, there's all sorts of possible causes - but increasing your gear ratio surely cannot help.