We (I for the blame sake) heard about drilling a hole in the ball valve to help drain the "slug" of water from the valve. It resulted in a quick change of the valve when we opened it. In our case the valve leaked through the hole when the valve was open. It was my idea I read about here and it just did not work.
If the valve does not need to hold fluid back then I would leave it open. If the valve does and there is a potential for freeze I would plug the source and drain the valve before leaving it closed. I use this method at our storage tanks (leave the plug in the bottom of the tank) and it works well.
Mike
Tapping since 1985 (four generations back to early to mid 1900s). 200-250 taps on buckets and then tubing in the mid 90s. 2013- 275 taps w/sap puller 25 gal. 2014-295 taps w/sap puller 55 ga. (re-tapped to vacuum theory) 2015-330 taps full vac. 65 gal, 2016-400 taps 105 gal, 2017-400 taps 95 gal. 2018-additional 800' mainline and maybe 400 new taps for a total near 800 taps. 2x6 Leader WSE (last year on it) supported by a 250 gph RO.