Is “of ” necessary in “all of ”? [duplicate]

Of is just a preposition used to say what group or whole includes the part denoted by the preceding word:

Example: most of/ one of/ several of my friends etc.

In the case of all, half, and both; of is optional and you can either omit it or keep it.

But you can't leave out of before the pronouns us, you, them, and it *.

^{*You don't need to worry about this with "both" because you're not going to say "both of it" anyway.}

Michael Swan says in his book *Practical English Usage:

1> All and *All of**

All (of) can modify nouns and pronouns.

Before a noun with a determiner (for example the, my, this), all and all of are both possible. American English usually has all of.

She's eaten all (of) the cake. All (of) my friends like riding.

Before a noun with no determiner, we do not usually use of.

All children can be difficult. (Not: All of children can be difficult)

No answer above is satisfactory.

I have answered this question in "All our X" vs. "all of our X", but let me rephrase here.

Listen to all of your fans
Listen to all your fans

"All of your fans" and "all your fans" are both correct. They are different in that in the first sentence, "all" is a pronoun, while in the second, "all" is a predeterminer that comes before the determiner "your", helping to further specify the noun "fans".

You may wonder the difference in the usage. A linguist explained, "[...]the variant without “of” is significantly more common than the variant with “of”, to such a degree that the variant with “of” might be considered unnatural (or colloquial) by some native speakers in certain contexts. My advice is: If in doubt, do not use “of” between “all” and another determiner." (https://jakubmarian.com/is-it-all-the-or-all-of-the-in-english/)

He explains better than Michael Swan.