Generally speaking: no. If you are truly shopping frugally, then you will be buying more store brands than the national brands and sites like Coupon.com usually only carry large brands, often all from the same company (e.g. mostly Quaker/Tropicana/Pepsi products, for example), which we rarely bought (also the main reason why we didn't sign up for Upromise, brands we just didn't use qualified and stuff we did use didn't). If you do buy those then by all means, print the coupon. If not....but the sites, if free, are good to keep around and check what they offer from time to time. If you happen to see a large brand name product on sale and it's a good sale, then that would be a good time to check and see if the coupon is available to take advantage of the discount.
If your grocery store uses a card or little keychain pass to get the savings at the checkout, check out their website. Kroger, for example, allows you to load virtual coupons onto the card (paperless coupons) that will be deducted at checkout should you buy that items. When we were living in the United States, Kroger was doing this also for store brands, but I just checked out the site now and that is no longer the case.
If you are not getting coupons via the Sunday paper, you can also get coupons from
(a) the actual package (look inside, they are often hidden and not indicated on the outside.
(b) from samples. I would sign up instead for free samples, from either sample sites or by just checking out the product online.
Hope that helps.