Surfaces Skimmers are perhaps one of the most left out filtration hardware, yet also one of the should haves. This is especially so if you own a pond. 

If you bother maintaining the sides of tank for a clear view, you definitely should maintain the surface of your pond. 
Fallen leaves, dead insects, uneaten floating food, stuff thrown in by the children, animal fur if you own some fur buddies, chemicals runoffs on the surface etc.. These are just some of what is captured by surface skimmers. 

Not only do they add on and potentially overload the bio filtration capacity, but these debris can also get unsightly. Very unsightly. 

Another benefit to these would be the elimination of dead spots, both in the water and on the surface. This would also help siphon off or prevent the laying of eggs by pest like mosquitoes, in this surface dead spots. 

Features,

• Must be connected to a pump to function well
• Can be connected to a pump in the pond filtration chambers
• Traps detritus and waste from the water surface
• Filter / Hang basket can be removed for ease of cleaning
• Extremely durable construct, build to withstand outdoor elements
• Base tray can be weight down with stones etc. 
  
• Potentially eliminate dead spots in the water and on the surface
• Potentially deter pests from laying eggs on the water
• Improved water circulation and aeration