What might sequence be needed for?

Question

MySQL

I understand that there is no sequence in MySQL... but sometimes they give an alternative implementation with an additional table.
The question is why this implementation is needed?

Answer 1

1) sequence is convenient when you need a unique id not only in one table, but in several. If necessary, it can be arranged so that the id is not repeated in all tables.
2) a common sequence for several databases. Helps to merge two tables from different databases and all have a unique id
3) etc.