I've been a Prime member for several years. I love it.
If you wanted to, you could replace your trips to the grocery store with online shopping. You can so many of the products you get at your local grocery and get them with free shipping. I don't do that, I mainly use it for bulk purchases on stuff like razors, soaps, cleaning products, etc. If you use Gillette disposable razors - Mach 3 or the like - you can get them a few dollars cheaper at Amazon vs. the store or Target.
I have also purchased small electronics such as a Yamaha stereo for our kitchen/dining area, clock radios, etc all have been quality products. I've never bought a TV or computer there but plenty of people have. Note that as a Prime member you get special pricing on items not available to the general public. For example, I can get $50 off a Kindle Fire HDX right now.
Finally, a very nice benefit is the 'Amazon instant video' - you can watch a bunch of movies and tv shows for free on your laptop, pc, Ipad etc. There is a streaming video app you can even watch on your phone.
I highly recommend Amazon Prime.