What gets pruned
Pre-aggregation makes each lookup cheap. Pruning is what keeps the search itself fast.
The pruning rules
Infrequent branches — segments below a minimum support threshold — are dropped early, since a segment too small to matter can't meaningfully explain a metric-wide change. The search also stops early once the ranking is stable, rather than exhausting every remaining combination.
The search is exhaustive within the cube's dimensions, not across all of mathematics.