Basically the rule says to not use equipment to arbitrarily slow speeds down for competitive reasons.
The rule says they can't charge more for faster access, among other things. Which is intended to prevent making "fast lanes".
It would have the interesting side-effect of making a sizable chunk of existing consumer plans unlawful, since most, if not all, ISP's offer several tiers of access - pay $50, get 50mb/s (or whatever), pay $100, get 75mb/s, pay gobs more, get 1Tb/s, that sort of thing.
As an example, AT&T offers five different rates for internet access, ranging from 3mb/s to 75 mb/s. So, four of those rate plans just became unlawful under the rule. Which I imagine would force AT&T to drop the four higher speed plans, since they can't provide all the speeds at every location....
While I doubt seriously the FCC has a problem with that, the fact that it's in the rules that they picked to enforce means it's available as lawsuit material just whenever someone decides to pull out lawyers against an ISP....