What is rapid signal attenuation?
You're misinterpreting that sentence.

There's no new concept introduced in 


  On the
  other hand, rapid signal attenuation with distance is also helpful; it reduces the
  interference between adjacent cells.


It's simply that if your signal quickly loses power over distance, someone else can use that same part of the spectrum e.g. for their own calls.

Given technical users per cell limitations, the operator of the cellular network needs fewer spectrum licenses when their signals don't reach far.