In some cases the owners of all the flats in a building co-own equal shares in the freehold. Typically, share of freehold homes are period conversions with only a small number of units, and sometimes the owners set up a company as an ownership vehicle for the freehold.
The owners are able to decide collectively how to manage issues like building maintenance. This can sometimes become fractious, but is usually considered preferable to being stuck under the control of a landlord.
The crucial benefit is that you can also extend your lease without paying a premium.
Because of this, share of freehold homes tend to be worth more than leasehold ones. The best share of freehold buildings are when owners collectively appoint a managing agent to help run and manage the building, collect service charges and have an adequate sinking fund in place to ensure the building is properly maintained overtime.