We should use composite character classes for the following reasons:

• To create new custom character classes from predefined Unicode blocks. For example, to match all the letters in an Arabic Unicode block, we can use the following:

[p{InArabic}&&p{L}] 

• To avoid potentially slower lookahead or lookbehind patterns by using the intersection or subtraction operation on multiple character classes.
• To enhance the readability of the regular expression.