If you stay Unregistered, you need not issue TAX INVOICE. However your buyer (if he is registered) needs to pay GST under Reverse Charge Mechanism. Then later your buyer can claim Input Tax Credit for the same.
If you are Registered, then you need to issue TAX INVOICE and comply with the GST filing, Eway bills and other relevant rules. Your buyer (if he is registered) can claim Input Tax Credit for the GST portion.
As you can see, all B2B Customers would prefer to deal with a Registered Supplier only, as they would not like to pass through RCM procedure.
Incase you have more B2B Customers, then it is preferable to get Registered even if your Turnover is under the limit mandated for registration. However if you have more B2C Customers, then you may register once your turnover crosses the mandated limit