Linked from
The 7 pages that link to Pollarding, each with the reason it gives.
PruningBroader topic: It produces recurring shoots from a deliberately maintained framework.
CoppicingCompared with: It also harvests recurring shoots, but cuts trunks well above ground.
HedgeRelated: Pollarding can maintain tall boundary trees without removing the hedge line.
ArboricultureCompared with: Unlike topping, pollarding is planned and repeated from an early stage.