It would depend what kind of situation your horse was going to be staying in. If you think you can keep the stall super clean (no manure stains) and have the time to possibly bathe/thoroughly groom before a show then you probably don't need a sleazy.
Personally I only put a sleazy on my horse when he's braided overnight so he won't rub them out and I don't spend an hour picking shavings from the braid LOL! But only if it isn't too hot, that's a big deal in TX.
My sister shows Western Pleasure/Hunter Under Saddle and her horse lives in a sleazy. She even lunges her in one. So it kind of depends on you I guess.
I don't show 4H, but I show frequently.
Neighs from Jayke and Buby!