Phrase "by twos and threes"

English as a Second Language English Vocabulary, Grammar and Idioms
1

I’d appreciate it if someone would answer my question. Thanks in advance.

Concerning the sentence, After 10 o’clock the guests began to leave by twos and threes.

Does “by twos and threes” mean “in groups consisting of two or three people”?

Does “twos” in the above sentence mean “groups consisting of two people”?

2

“Yes” to both questions.

3

—Thank you Milanya.
I’d like to ask one more concerning the above question?

Is the substitution by “twos” (instead of saying “groups consisting of two people”) for economy of words?