What is the "Shaped Charge" (LW2) supposed to be good for?

Yes, it's exactly for extreme environmental damage!

It destroys pretty much everything (except maybe some load bearing pylons) but it has a very short range so it's kind of a high risk - high reward situation.

I usually use it when I have enemies concentrated in a spot, behind heavy cover, who just won't die. I approach, expose my soldier and throw the grenade betting on the fact that I will absolutely kill everyone after they're exposed! (risky bet)

You can also read about The Shaped Charge in real life.

The Grenadier grenades are ideal for combat but they don't always destroy high cover. Shaped charge is ideal for a specific task. Jails usually have few entry points and sneaking your squad as close to the objective as possible before breaking concealment is ideal. Getting your squad into position and using this tool can make ambush and run or no fire tactics more viable for an extraction.