Before serviced offices existed, you would have taken space on what we refer to as "conventional" lease terms. This would involve a long legal document (with advice from your solicitor) and the offices would be unfurnished. You would be responsible for all of the maintenance including heating, lighting, cleaning, repairs etc. and you would have to return the offices to their original condition before giving them back to your landlord at the end of the lease. No furniture or equipment would be provided by the landlord - you would effectively be leasing a shell, ready for you to fit out. In the UK a conventional lease used to be for as long as 25 years (although this is shorter now) whereas in Europe a lease would typically be for 3/6/9 years and in the USA for shorter periods of time. Conventional Offices still constitute the largest part of the commercial property market today.
A "serviced office" is the type of office normally found in a Business Centre. The term differentiates this type of office from a Conventional Office in that many additional occupier services are provided within an inclusive rent over and above those normally associated with a conventional office. In general, a serviced office rent will normally include business rates, receptionist services, furniture, heating, lighting, air conditioning, cleaning, maintenance, cable networking etc. Therefore although the rent might look higher to begin with, when all of these additional costs are included it easy to see that the rent represents good value for money because these services are bought at bulk prices by the serviced office operator.
The rent for a conventional office is typically expressed at a cost per square foot per annum eg £45 per sq ft. The rent for a serviced office is normally (but not always) expressed as a cost per workstation per month eg £500 per workstation. To try and compare these numbers isn't straight forward - remember to differentiate betwen apples & pears!