What a tag is for
A tag is a label on a member that you can filter by later. On its own it changes nothing; it becomes useful the moment a decision depends on it, such as who gets a message, who skips a restriction, or who you look at when something goes wrong.
What is worth tagging
Only what changes your behaviour towards someone. Customers, so you can reach the people who bought. Moderators, so the list exists outside your memory. Paid or VIP members, so access is a label rather than a favour you remember. Tagging hobbies or regions is tempting and usually becomes stale data nobody trusts.
VIP and verification, and how they differ
Verification confirms a member is who the group requires them to be before they get full access. VIP management is about giving a defined set of people more than the default. One is a gate, the other is a privilege, and groups that use the same mechanism for both end up unable to explain either.
Keeping tags honest over time
A tag is only as good as the last time it was correct. Decide when a tag is removed, not only when it is added, and tag through a rule where you can rather than by hand. A label that ages badly is worse than no label, because people act on it.
What this is not
Tags are not a CRM. They label members of a Telegram community for moderation and messaging, and they are not a place to record notes about people. If you need customer history, the shop's orders already hold it, and keeping two versions of a person in two places is how they start disagreeing.