|Do you know where your variables are?|
The only reason I can think of for turning them off completely is to try and gain a little performance once you've completely debugged the program.
I tried this a few times in the past and found that it rarely, if ever, made any significant measurable difference.
Conversely, I almost always found yet another code or algorithmic change that would speed things up; but I always had to re-enable B&D to find bugs introduced by those changes.
(My) Bottom line, I always turn them on when I start a script, and for the last 8 years or more never even think about turning them off, except for very small scopes.
With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority".
In the absence of evidence, opinion is indistinguishable from prejudice.