I wouldn’t. The shipping is a service charge. If I can avoid a service charge by clustering together things that I would be buying anyway, I’ll do it.
When you place an order through Amazon, it gets delivered to your house, meaning it will be shipped regardless of whether or not you’ve paid an extra charge for the shipping. I think it’s really silly to pay for shipping when you don’t have to, unless of course you’re paying for the convenience of having your item shipped to you right away rather than waiting until you need something else. (Even then, I’d rather stock up on things I know I will need eventually. Pay now or pay later, I’ll still be buying them at some point, so it’s not really spending “extra” money to buy them a few weeks early.)