As a landlord, you have a legal requirement to have an annual gas safety check and provide a certificate as proof. The inspection should be done on all gas appliances in each of your properties, and you should receive a copy of the certificate to keep for your records, as well as providing a copy to your tenants.
As a homeowner, you are not legally required to hold a Gas Safety Certificate but it is strongly recommended to have an annual check or service of your gas appliances to check they are working safely and efficiently. It is worth noting that some home insurance policies require Gas Safety certificates for policies to be valid so it might be worth checking with your provider.
It's also worth noting that having an annual service is also required to ensure the validity of your boiler warranty.