...why does it say this in the rulebook if there's no more fettered power?
"
By minimising the amount of power he draws, a psyker
can reduce the chances of horrible side-effects such as Psychic
Phenomena or Perils of the Warp
(see page 195). When using a
psychic power, the psyker must choose an effective psy rating for
the power that is equal to or below his base psy rating. This value
must be at least 1."