Sec 44AD is optional or Mandatory?

Pushpadantha (Articleship Student) (44 Points)

24 July 2017  
By reading the sec. 44AD(1) it looks like 8% of the turnover is deemed to be the income of assessee whose turnover is less than 2 crore.

Therefore, is it binding on all the assessees automatically or is it an option?

Please confirm along with the provisions.