GST registration is compulsory if your turnover cross 20 lakhs. In other cases it is optional.
If you need GST registration, you are free to take it.
However whether you should take GST registration or not depends on many factors (No choice once turnover cross 20 lakhs, 10 lakhs in special states).
- If dealing in B2B clients then GST registration should be preferred as registered person under GST will not prefer business with an unregistered person.
- You can avail input credit of taxes paid on inward supplies.