he actually has a lower jump height than Sonic or Tails, and there are basically bits of level design that were woven into the Sonic 3 Stages (which you could not play as knuckles without S&K) that are behind breakable walls only Knuckles could get behind, or that you'd have to use the debug tool in Sonic 3 to get to with sonic or tails. (NintendoWorldReport.com)
A surprising thing about Knuckles is that he doesn't require a spin to breakthrough walls; he can charge through breakable walls by just running fast enough. (thatvideogameblog.com)
In the later levels the game introduces breakable walls and obstacles such as sawblades and baby birds with gems in their beaks. (gamergeddon.com)