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Ignoring the other benefits to prime outside of shipping, this is a major caveat:
"Amazon still ships free when your cart is above $35, albeit a few days slower. "
Most people are fine with slower, but if you're forced to make your order $35 to get free shipping, you're likely buying stuff you don't want/need just to get to that amount.
Just to save like $10 a month?
I don't think you save money by cancelling, unless you actually don't buy stuff from Amazon to begin with.
For me, having Prime is still worth it. Several grocery items are still cheaper from Amazon, and ordering for same/next day means I don't have to waste time/money/energy going to a store to get that same item.
But that doesn't mean I won't cancel the moment Prime stops being a good value.