In Zoom, there are two different types of meetings: Personal meetings and Scheduled meetings.
Personal meetings are catered more towards instant access to the host. These are more appropriate for office hours or impromptu meetings. Personal Meeting IDs remain the same through the life of the account.
As for Scheduled meetings, they are catered more towards bigger audiences and at a specific time. Class meetings or important staff conversations are more suitable for these types of meetings. Anytime a link is to be shared widely, either online or via other methods, it is wise to choose a scheduled meeting as this Meeting ID and meeting information changes every meeting.