If you read my whole post, you'd note that I said my hose is on a reel.
The cap simply prevents any dripping while the hose is being reeled up. No need to carefully hold the hose end up high with one hand while you try to roll up the hose with the other. No worry that any movement of the hose will push any liquid out that end (and potentially on you). The other end is still in the cleanout, so no concern about drips there.
Once the hose is reeled up, you can then remove the cap, holding the end of the hose higher than the reel, and let any final draining happen at the other end. Then pull out that end from the cleanout. Done.
No walking hoses 50+ feet, no drips. Takes seconds to put the hose away without drips.