Don't focus blobs of hp. Always primary high threat targets
So enemy team has Tahm Kench Top, he's used devour. He might stun your toplaner for 1 sec after autoing them 1000 times. Do not waste one auto, one damaging ability on him, not even the stray ludens proc.
Just walk around him.
Other blobs of hp are: Sion, Garen, Cho'Gath, stuff will little CC or CC that is avoided by flash or high movement speed
Other blobs of hp are champs that are behind and deal 0 damage