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A CRM is one record per customer and per opportunity, holding who they are, what was said, what was offered and where it got to. Everything else a CRM sells you is built on those two objects.
The definition is unhelpfully broad because the category is. A shared spreadsheet meets it; so does a system running a bank.
The honest purpose is not reporting. It is that the next person to touch the relationship — a colleague, a successor, delivery, finance — can find out what happened without asking anyone.
Everything valuable follows from that: a forecast that can be checked, a handover that does not need a meeting, an account history that survives a resignation.
For one person, effectively yes. It stops working at the handover, not at the arithmetic.
Only once more than one person needs to know what happened. Before that it is optional.
A record that takes from the people updating it and gives nothing back.
Half an hour with your own data usually saves reading three of these. The guides will still be here afterwards.