40D Owners: Focus search on/off?

Curious to now is you leave this Custom Function set to default On or set it to Off.

After having sometimes erratic misfocusing with my 70-200 f/4L where on occasion a series of photos would be maybe 5 out of 10 out of focus. In my initial testing with it Off the issues seem to have gone away. Oddly it never showed up in any of my other lens, just this one which had always been dead on with my other bodies in the past.

Thanks

I thought that it would be useful to enable that until I encountered two lenses that refused any attempt to focus as a result. If it works for you, particularly if it cures a problem, then use it. I just have to live with very occasional hunting in poor light or low contrast.