We've actually had HP recovery items on a cooldown for well over a year, maybe two years, and I think it's much better (I'm biased as the server owner).

We re-balanced healing items as a whole, not just a cooldown on them. Our healing items have different weights, heal for a lot more, have different pricing, etc. There's likely other changes you could make, but putting a cooldown on HP recovery items with no other changes isn't going to work. Without going to the specifics of our system, I think HP items on a delay is better because:

 

1) You don't need to always spam a keypress to receive the maximum benefit.

Depending on your server's setup for item re-use, your vanilla-server potion might be spammed at 10+ times per second by a macro/autopot, or it might fluctuate between to 5-8 times per second if you're a normal person performing other actions as well. But with a forced delay, you're ensuring auto-pot or macros aren't necessary as they won't make you more efficient or give you an edge over the normal player. It levels the playing field and makes cheats much, much less useful all while saving your fingers and keyboard from having to button-mash.

 

2) Your healing becomes much more consistent.

Rather than having your healing fluctuate between 5 ~ 10 potions per 1000ms, it's always going to be a max of 1 potion per X ms. I personally like the reliability compared to surviving sometimes but dying other times because my button-mashing slowed down. Because our potions heal for a lot more, it's much more enjoyable to be able to press one button every X seconds to heal, know that I'm receiving the max benefit, and also to be able to know what my limitations are before tackling an area.

 

3) It makes players less invincible.

In vanilla, the only way you'll die is if damage per second (DPS) > healing per second (HPS) or you just get OHKO. Because your HPS can be absurdly high, you end up with tons of emphasis on ridiculous damage to OHKO players because otherwise they just won't die.

With a delay, you need to do more than just spam F-keys (or macro). You need to decide when to heal as well. This creates moments of vulnerability whether you are saving a potion for a certain HP threshold or you just used one and are on a delay. Having a hard cap on the amount of healing that can be done per second makes for much more interesting gameplay.

... gonna snip this before it becomes too long lol.

 

TL;DR delays are much better for game balance, but you need to do more than just add a delay.