Unsure why this is so downvoted? Several banks support turning off the overdraft feature, which just causes debit transactions to be declined (or ACH items returned).
What about NSF fees? The NSF fee at my bank is 8x more than the overdraft fee ($40 vs $5 + 20% APR). Turning overdraft off would be a poor choice for me even if I anticipated the occasional overdraft.
The problem is that those features don't always work if multiple pending transactions have been submitted, or if checks are used, transactions ordered a certain way (some banks have been in trouble for doing this in the past), etc.