Confusion about when it's my navigation, and when it's ATC

Pixel Dent writes:

3. The term "cruise" may be used instead of "MAINTAIN" to assign a block
of airspace to a pilot from the minimum IFR altitude up to and including
the altitude specified in the cruise clearance. The pilot may level off
at any intermediate altitude within this block of airspace.
Climb/descent within the block is to be made at the discretion of the
pilot. However, once the pilot starts descent and verbally reports
leaving an altitude in the block, the pilot may not return to that
altitude without additional ATC clearance.

I think I read this section before; this paragraph sounds familiar. I
always get instructions to "maintain," though. What's the phraseology
when I get a block of altitudes? Or does it even happen with
frequency in real life? How do I request it (or do I even need to
request it)?

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