The Lily Pipes have several functions IMO
1. Cosmetics (especially in an ADA style tank)
2. Vortex - Because of the unique shape of the lily head it creates a whirlpool effect. The whirlpool acts as a skimmer; the whirlpool creates a suction causing surface oil to be pushed down and sucked into the filter.
3. Slow down flow- Because the lily head is so wide it allows water to flow out at a more gentle rate. (preventing uprooting)