The “equal to” operator = returns TRUE when the two arguments have the same value.
This operator does not perform any implicit conversion between strings, numbers, and Boolean values.

The following comparisons always return TRUE:

• A comparison between BLANK and 0
• A comparison between BLANK and an empty string
• A comparison between BLANK and FALSE

This comparison differs from == only when at least one of the two terms is BLANK.

The following are valid expressions using the “equal to” operator.

Product[Color] = "Red"
Product[Color] = BLANK()        -- Returns TRUE if Product[Color] is either BLANK or an empty string, otherwise returns FALSE
Product[Color] = ""             -- Returns TRUE if Product[Color] is either BLANK or an empty string, otherwise returns FALSE
Sales[Quantity] = 1
Sales[Quantity] = BLANK()       -- Returns TRUE if Sales[Quantity] is either BLANK or 0, otherwise returns FALSE
Sales[Quantity] = 0             -- Returns TRUE if Sales[Quantity] is either BLANK or 0, otherwise returns FALSE
Customer[LargeFamily] = TRUE     
Customer[LargeFamily] = BLANK() -- Returns TRUE if Customer[LargeFamily] is either BLANK or FALSE, otherwise returns FALSE
Customer[LargeFamily] = FALSE   -- Returns TRUE if Customer[LargeFamily] is either BLANK or FALSE, otherwise returns FALSE

The following expressions return the same result using different comparison operators.

-- The following two expressions return the same result
OR ( <exp> == 0, ISBLANK( <exp> ) )
<exp> = 0
 
-- The following two expressions return the same result
OR ( <exp> == "", ISBLANK( <exp> ) )
<exp> = ""

See Handling BLANK in DAX for more details about BLANK comparisons.