Question

Of what value are constellations to the modern day astronomers?

Answer 1

You can compare them with countries in geography.

Explanation:

If you want to give the general position of an object in the sky, you name the constellation it's in. You may even name the star that it's close to (compare cities on a map).

But if you want to be precise, you give the numerical position (just like GPS-coordinates on Earth).