With less than 2 strikes, you don't want your batter to just be swinging at strikes. You want them looking for a pitch in their favorite hitting zone.....something they are looking for prior to the pitch even being thrown.
There are also situational reasons for not swinging until a strike is called:
1) Pitcher has just thrown 9 pitches in a row outside the strike zone
2) Your team is down a couple of runs in the last inning.
3) First pitch changeup you're not looking for
As a rule, I cut my hitters loose and trust that they will implement the hitting strategy they have been taught. I also don't give hitting lessons during an at bat......like many others I see.