The advantage of holding the freehold of a property are much the same as in the residential market.  As the sole owner all decisions on the future of that property are yours.  You are also responsible for all repairs and maintenance. 

Buying premises is a major investment for any business.  In the long term this investment could give you a good return as it generally works out less that the rent you would pay.  The overall cost of buying premises is usually higher than renting for the first five years, equal for the second five and cheaper from then on. 

You must also consider how easy you will find a buyer for the property when you come to sell it.  Alternatively you may consider becoming a landlord and lease space to other businesses. 

Useful Websites
 

The Office of the Deputy Prime Minister is responsible for policy and legislation for business tenancies - its website provides guidance for businesses thinking of taking on a lease or a freehold.  There is a useful 'frequently asked questions' section.