Nothing is written in stone (Probability Theory & Utility Theory)
Probability Theory
The Basic Strategy is right -- and is the standard rule in BJ. But it tacitly assumes that your goal in playing the hand is to maximize your expected return on the bet.
Utility Theory
There may be circumstances under which I have a goal other than to maximize the expected return on that specific hand. In such a case, deviation from the Basic Strategy may be the right thing for the moment.
Here's an example from my own play last night. I'd been playing for about 2 hours and couldn�t put together a substantial win, the Bankroll was hovering up and down +/- $500. Finally, while being on the plus side of $$ I decide that I should end the session. Well, the next hand I get was a BJ (T,A), the dealer had an ACE showing. My goal at that point was simply to break out from the game. I declare �even money� regardless, even if the count was down the tubes into the negative, I don�t care! .., Emotional victory is more important vs. making an additional half a unit. That half bet was far too low reward for the possibility of having a push with my BJ vs. dealer�s BJ. Buying insurance was the correct move under the conditions stated above since I locked up the chips for that bet and left the game.
Now, in a different circumstance I may play that hand differently.
Getting �even money� on a negative count is a losing move overall. But it is a tactic that many be used for another reason. Depends upon your attitude towards the game, and other factors as well. It might take years for the disadvantage of the play to actually cost you any money on this move alone.
As usual, Basic Strategy is not always cut and dried. Nothing is written in stone.
Making money is the name of this game!
Sonia