Landlords, letting agents and repeat clients rarely have just one property. Your records shouldn't pretend they do.
A single customer record works fine when someone has one house and one boiler. It falls apart fast when that customer is a landlord with eleven rental properties, a letting agent managing a portfolio, or a repeat commercial client with three sites across town - all needing separate histories under one relationship.
The problem with flattening everything into one record
Without a proper structure, either every property gets its own separate customer entry (duplicating contact details and losing the bigger picture), or everything gets crammed into one messy record where it's unclear which job happened at which address. Neither is a good option when someone calls asking about "the flat on Elm Street" and you're trying to work out which of eleven that is.
What proper property management fixes
Multiple properties sitting under one customer relationship, each with its own job and service history, means the full picture is there without the guesswork - genuinely useful for landlords, letting agents and any business with recurring, multi-site clients. It's a small structural difference in the customer records that saves a disproportionate amount of confusion later.
The verdict
One customer, six bathrooms, is a completely normal thing for software to handle. It's an unreasonable thing to ask one person's memory to.