Writing comments is very important that it helps others to understand it easily.

E.g. 

You have written 15-20 lines of complex DAX Code for Client ‘C1’ on the particular requirement and after few days you have switched to other Client ‘C2’.

Within few weeks after you joined C2, C1 clients reach you and needs code CHANGE in DAX which you earlier have given to them, however, a few weeks back, you were in full swing, wrote the code and you have not written single line comment in your DAX Code about to logic used or variables used or conditions used or functions used or columns used or measures used or tables used ETC. 

Now you have to again SPEND your time in parsing old code and you are completely lost in complicated code.

Finally, you will learn a lesson from the above Example that “Comments” are very important even if you want to understand your own code after a period of time you need to Read Comments.

Now in Power BI, we have Single line commenting and Multiline Commenting:

Comments are BASICALLY Green in colour.

• Single line commenting
  • We can use two Hyphens or Dashes or Minus sign to comment a single line

(OR)

• We can use two forward Slash to comment a single line
• Multi-line Commenting
  • We have to use forward slash followed by ASTERISK sign for beginning and to end asterisk sign then forward slash.