Is NCT a must even if the car will not be driven ?

No, it's only a legal requirement if you drive on public roads

So what do you need the car for if it won't be driven?

Sell it and get some money back.

Where will the car be parked / stored ?

How long will it not be driven for? Because the NCT is done by registration date not when presented so unless you are parking it up for longer then a year, or 2 if it's less than 10 years old, there is no benefit to not getting it tested.

Once it's expired you can't drive it on the road so you will have to get it towed to the test center.