importance of horn of renew in PVE

Long time ago, When i played my rogue and mage, I used combat medic/ lifegiver in PVE, I was blamed for wasting a skill slot to deal damage. Then, they asked me to use pots instead.
But I see horn of renew is a must-have skill for every warrior in game/ forum.
Sorry for ignorant. Why dont they use pots to replace horn of renew? Even without invulnerability from HoR, a warrior can still survive from the attack of boss. You can taunt with other skills(windmill, CS ,AX,jugg). Is this skill really that important?

I have played with tanks that don't use it. For the most part I don't need it and would rather use a combo if jug and vengeful blood. How ever it does save the team at critical points. With good timing it makes a big difference. So for me I always use it to help the group more then just to heal me.

When tanking I've found that while your skill rotation can maintain most of the taunts, Horn does more than just taunt in my opinion. Timing the shield and heal on your party can make a difference in maps where you can then do big pulls of mobs, while maintaining tank aggro and letting the DPS classes go all out on the mobs.
As Capeo mentioned, its often more about keeping the party alive so that they can do what they do best.

Because Elites. I'm not sure how it is for you guys nowadays, but if I remember correctly, last time I played elite mobs can still one hit rogues and smurfs. The short invulnerability makes a big difference in tanking, ESPECIALLY when you're taking elites seriously. Every run should be smooth, less pot burning as it should be.

If you put mastery points on horn then your party gets increased armor for the duration of the skill. This is beyond the heal and the shield. This skill is critical in maus, IMO.

Unless you are running solo always use horn of renew with all pts in it 5/5. Always charge it so you get the the protective shield. It will keep your team alive in the first 3 seconds of a fight and give you time to start controlling the mobs. Also good for timing with red zones on boss and some mobs too. You don't really need it in easy elite maps if you're doing aps but in mauseleum and higher elite maps always use horn. It's not about keeping yourself alive tanks are pretty hard to kill but more about keeping the dps classes alive so they can kill easyer and faster.