A whole lot! Receivers don't put out the same kind of power (and tests have PROVEN THAT FACT!) that separate amps do and the vast majority of people can hear the difference!
I'm sorry if you and others can't hear the difference, or just choose to rely on specs & tests to tell you what you should be hearing. Or simply decide for the sake of saving some money that a difference isn't made.
But you shouldn't be telling the rest of us that we are NOT hearing what we hear, or we are crazy for hearing it since you obviously don't hear what we hear.
What I find ironic is if the pros on here decide to test speakers they ALWAYS use separate amplification. That alone should tell you something, but you CHOOSE to ignore that little bit of information & still insist that ext amps don't make a difference!
If you choose not to use separate amplification, that is your choice & you are free to do so. However, if someone comes on here looking for amp recommendations, at least have the curtesy of staying out of the conversation if you have nothing but negatives to add.
As the old saying goes. If you have nothing good to say, say nothing at all!
Now if you have knowledge of constant equipment failure from a certain brand etc, then by all means a warning to that effect would be in order.
In some ways, those of you who decry the benefits of amplification so vehemently and harangue those looking for advice about it, remind me of the useless people who scream at women going into clinics that also happen to perform abortions.
It doesn't affect you, or your wallet so what do you care? You have your truth, and they have theirs.
It is their money, let them spend it as they wish. Live & let live folks!
What, pray tell, does power have to do with the "full potential" of speakers?