You can build it with Bramble Vest, Morellonomicon, and Executioner's Calling.
It's incredibly useful against the likes of Soraka, Dr. Mundo, and Yuumi.
No, you don't need to follow your mobafire build to the letter when you do less damage than the enemy is healing.
Grievous Wounds is also useful against:
Healing is a lot more prevalent than people realize. The reason why the pro builds don't tend to include grievous wounds is because at that level of play, fights are decided quickly, but they have relatively low-kill games. In lower tiers, fights are messy, and people have a tendency to overstay.
The optimal build is only optimal when people are playing the games optimally. The build that you get from op.gg is not going to be the best build in every Iron II game.
Tell it to the ADs of the team especially. It's annoying to see ADCs/Bruisers/Juggernauts/Assassins complain about healing while being unwilling to spend 700g for anti-healing. Bonus points if those same players have the audacity to suggest you build Morello. Worst yet is that mages are suggested to build Morellos far more often than ADs are suggested to build Executioners.
just remember to never complete thornmail because that item sucks
Take this advice with a grain of salt as well. It's not as incredibly useful against 
as OP says it is most of the time.
I see a lot of ADCs who are losing against a in lane waste their gold on 
and then lose even harder. The thing about is she can also be a bit of an early game bully against certain match ups. Her heal makes little difference early game. If you're focusing on that early game, then you're probably going to be under tower again soon enough.
What you want grievous wounds for is exactly what the first poster pointed out. There's a lot of champions with insane self-healing right now due to items and runes, and we're in a meta where everyone does insane damage so items like 
and 
are so deadly and can make those high damage dealers almost unkillable.
It's like they have 2 's on them. That's why you want grievous wounds, but yes it's also good against healers later.
i mean who doesn't build morellos tho?
