Pivot Shoe

If your shoe is too shallow for the track, then there is the possibility that it will wobble as you operate the window. Even as small a difference as 1/32" could be noticeable. It may also have issues locking in place when tilting the sash in for removal; if the brake can't make full contact with the track, then there is a chance the shoe will not lock properly and therefore shoot up in the track when you attempt to remove the sash.

My rule of thumb is always to replace the old hardware with exactly what was installed originally. If you feel that the window is dragging too much, then you might want to consider lubricating the track with a silicone spray to help loosen things up.

Of course, you are free to use the 1/2" shoe is you feel it's the right call. I just want to make you fully aware of all potential consequences.