Eheim Ecco Canister Filter 2234

[This Old Spouse]

I was just looking on another site and saw that someone was using a pre-filter with their 2234. At the risk of sounding like a complete idiot yet again, could someone tell me why this would be necessary or favorable?

 

[Juggler75]

to protect fry/shrimplets? probably wrong but thats what I was told they were for.