Typically it can be driven by the need to comply with:
Quote:
CS 25.841 Pressurised cabins
(a) Pressurised cabins and compartments to be occupied must be equipped to provide a cabin pressure altitude of not more than 2438 m (8000 ft) at the maximum operating altitude of the aeroplane under normal operating
conditions. If certification for operation over 7620 m (25 000 ft) is requested, the aeroplane must be able to maintain a cabin pressure altitude of not more than 4572 m (15 000 ft) in the event of any reasonably probable failure or malfunction in the pressurisation system.
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The emergency descent capability is combined with the rate at which the cabin depressurizes for the various failure cases, and the net cabin altitude has to stay below 15kft. If the a/c only just passes the check with full spoilers, then it'll fail with partial spoilers, unless the altitude at the start is lowered.
There may be additional guidance (AC, AMJ, etc) giving more details. I haven't looked into that.
