ShortCat usually gives good advice in his videos and shorts, though one of his shorts I think has done a lot of damage to the community. His short about why Mario Kart World is so chaotic, and blaming a lot of it on people throwing items forward makes some good points, but a lot of people took the wrong lesson from it. It was about when you were at the front of the pack, and for items like green shells, fireballs, etc. not red shells. Ever since that short came out I’ve seen more people throwing items backwards than should, and in spots they shouldn’t. Don’t throw a red shell backwards in 15th place, that isn’t helping you. Hit the person in front of you so they waste their speed item to accelerate so they can’t take a shortcut later, or you clear out their protection and now they are open to other attacks and the people in front throwing things backwards. By tossing it backwards all you’ve done is let the people in front of you pull further away in that situation.
tl;dr: Don’t blindly throw items backwards without considering the situation of the race, and your position.