Why do people put air pump in their sponge filter?

[WeepingCrown]

I've been noticing more and more that people put their air pump tubing into their sponge filter instead of putting their filtration tubing around it. I understand that the bubbles exiting the filter allows for water flow through the sponge but wouldn't it be better and more efficient to just use a external filter with tubing to suck water through the sponge?

W

 

[fishwonder]

Either way will work. Air pump and sponge is just cheap and the best filtering possible is a sponge. Can't really beat it.