I think that's just for counting nouns using the numbers. 1 dog, 2 dog, 3 dogs, etc.
When addressing more than one person or a person more senior, you use a special polite / plural command by adding '-ibh' or '-aibh'.
Thigibh a-steach, a chàirdean. - Come in, friends. Thigibh a-steach, a sheanair. - Come in, Grandad.