The free two day shipping means I order more household supplies. When I am getting low on something like toothpaste, deodorant, toilet paper, etc I can just order it instead of wasting time at the grocery store.
I have had prime for years for Free. You just need to find the right promotion. Right now I am on a 6 months free student promotion using my .edu address. When I signed up for it I was taking a class at LSU. Before that I was an amazon MOM for 18 months for FREE! It was a 3 month promotion at the time, but there were ways to extend it. Any Amazon Mom purchase over a certain amount extended the promotion, but you could add say a $2 bottle of baby powder to a $100 of whatever else and it would all count as an amazon mom purchase and extend the free prime. Before that I was just on the free prime trial and it would extend on its own every time I when I would go to cancel, I guess I spend too much money on amazon, just don't tell my "Big Box Retailer" employer.