Some cars are equipped with anti-knock sensors and will retard the timing to compensate for inadequate octane.
I'm not sure I'd want my engine running in a degraded mode.
Fuel ain't cheap, but in the long run, good fuel can make a difference. My owners manual calls for 91. In my area there's 87/89/93. I use 93 - wouldn't think of feeding the car anything less, irregardless of what was said in any magazine article.