In Expression, is it necessary to have square bracket [] for variables ?

[LauChuanLi]

I am copying codes from other software; hence I wish to explore if I can skip the step to add a square bracket for each variable.
I have tested to run without square bracket, and it seems like no issue. Thank you. 

[Rahulv288]

It won't cause any issue, but it will be good practice to use brackets.

[binuacs]

@LauChuanLi The variable should work without a square bracket if there is no space in between