if you send a recycler with your fleet does it automatically pick up some debris, because I see ppl quite often send recyclers with their attack fleet and was contemplating exactly how dumb they are... or if there was a purpose.

They use the recyclers to slow the attacking fleet so that the attacking fleet would have the same speed as the recyclers. You can time the attack and the recycle mission easily.

Ah now i see, thank you

Just a quick note, if you think the person may log on soon, you may want to manually time the Recycler fleet/attacking one, that way the Attacking message isn't shown for very long.

on big targets is better to send the recyclers ahead of time and send fleet at 100% timed correctly this way there is less chance an ally will acs defend

Yeah that's what I normally do