When should variables be concatenated using the dot (.) operator in PHP, and when is it not necessary?

Variables should be concatenated using the dot (.) operator in PHP when you want to combine the values of two or more variables into a single string. This is necessary when you want to create a new string that includes the values of the variables. However, it is not necessary to use the dot (.) operator when you are simply outputting the value of a variable within a string using double quotes. In this case, you can directly include the variable within the string without concatenation.

// Concatenating variables using the dot (.) operator
$var1 = "Hello";
$var2 = "World";
$combined = $var1 . " " . $var2;
echo $combined;

// Outputting variable within a string using double quotes
$name = "Alice";
echo "Hello, $name!";