A flat is almost always leasehold, but where the leaseholders collectively own the freehold — typically via a management company in which each flat has a share — they control the building, set the service charge, and can grant themselves long lease extensions at nil premium.
The practical benefits are real: no third-party freeholder extracting ground rent or inflated charges, and the ability to extend a short lease cheaply, which protects mortgageability and value. The trade-off is responsibility — the owners must run the company, insure the building, and manage works and disputes between themselves.
Buyers should still read the underlying lease (its term and terms still govern day-to-day rights), confirm how the freehold share transfers on sale, and check the company's accounts and reserve fund.