The ash content is the amount of ash that is left after the burn is completed. The level of ash aloud is also set by ENPlus A1 standard. The level is set at <0.7% allowable ash per Kg of pellets burnt, which translates in to a typical household generating 35 Kg of ash for 5 tonnes of pellets burn.
The ash content is important because you are left to dispose of the residue, the garden is an ideal for place for this as it can be used as pot ash.7