It was a bad idea on many levels, as it was "restriction" only designed to send out some-sort-of half-assed message about environmentalism which really, really didn't come across well.
It was further neutered by the fact that the Warp Factors mean nothing to us because no matter what warp speed is mentioned we know it'll work as fast as the plot needs it to. If the plot called for it Warp 5 would get the Enterprise from the edge of Federation space back to Earth inside of a couple of days (when it "reality" it'd take months.) So there was no point to it, especially since before too long a "solution" was found that didn't cause the "environmental damage" and didn't require the warp-speed limits.
So it was a bad idea because it was invented only to preach and it was never really obeyed or followed up on and ultimately meant nothing since as far as what we see in the show is concerned the Warp Factor means nothing to us. Beyond we know that "Warp 9" is really fast and "Warp 5" is sort of slow.