Applying for ANY new credit is going to "ding" your credit score. But if you are not over your head, pay your balance off monthly, and watch your total "available" credit limit on ALL your cards, then your score will recover and using the cards in the right way will actually increase your score. Also, the "ding" for applying for a credit card will depend on how often you apply, how much you credit you receive, and how many outstanding cards you already have.
If you have a great credit score, in the 700-800 range, then a temporary 5 point ding isn't going to make a difference in your ability to obtain more credit. If you are going be shopping for a mortgage in the next year or so, you may want to hold off on applying for any new cards. If you are established, and have all your financial ducks in a row, then applying for a store card makes sense.
The most important thing to do is pay off those cards every month. This keeps me from overspending. The perks you get from using a store card are well worth having the card, IMO. Also, you can use a BR card at Gap, ON, and Piperlime. So that's actually a smart card to get.