My answer is, if you do have some extra money, saving it into TFSA doesn't hurt you at all. In general TFSA has higher rate than other regular saving accounts, and famously, tax free. Even low income families don't pay much tax, you won't get hurt on tax free. In addition, if you need money for any reasons, you can withdraw at any time, without panalty. I don't come up with one reason why not opening a TFSA, maybe I'm not enough 懂行.
Some people may say, RRSP can deduct taxable income to save tax, while TFSA can't. Yes, it's absolutely correct. But, we all know, we eventually have to pay tax for RRSP when we get that money out for living (retired). If your current tax rate is lower than the later time (say 20 or 25 years from now), and it's going to be very likely, in fact RRSP losses money. TFSA won't hurt you and your money at any time, now or later.
Of course, for each individual one, which saving is better, RRSP or TFSA, it's a very good question. There are tons of discussion on this topic searchable on the web.