Models which are lapping round the flank or rear are ignored for purposes of establishing a unit's rank bonus in hand-to-hand combat. Lapping round models in this way might therefore reduce your rank bonus by reducing the number of ranks fighting.

However, units which are lapping round do receive the extra bonuses for flank and rear attacks so long as the entire unit consists of five or more models. This means that in most cases it is well worth lapping round where vou can.