Fretting Scales - Ascending problem

when doing an ascending run on a scale, from bottom to top, high e to low E. do you put your fingers onto the fret then hit the note, or have your fingers aleady there and hit the note and take your finger off? I read somewhere that this is the way to do it, but I dont do it that way, I do descending the same as ascending, putting my finger on the fret when its needed.??

thanks

I don't put that much thought into it, I just play it. as I understand it, you want to keep your fingers close to where they're going to end up (more efficient). Basicly, while you have a string fretted, it can make noise, so it's best to keep it fretted only as long as you need it to be.... ah.... I really don't put much thought into this at all... I hope I haven't confused you