I understand that it oversaturates target machine with external communications requests, such that it cannot respond to legitimate traffic, or responds so slowly as to be rendered effectively unavailable.
Once computers recognize where the requests are coming from they block them. Blocking; however, still slows down a computer. Why does blocking slow down a computer?
Moreover in the case all of the requests are coming from one port why does it still slow down a computer to block that port?
The switch/server still has to inspect the frame to know whether to filter it out. Thus filtering has some overhead even if it's blocked.