Managed IT services means that all IT and related services (such as computers, servers, printers, telephony, broadband, website hosting and so on), is supplied and supported by one provider. This can simplify the perception of support as there is only one company to contact for anything IT-related.
Delivery of Managed IT support normally means that the provider will subcontract some or all the services you require to 3rd-parties and then re-sell them under their own name. You have no access to the company actually providing the support.
The alternative, 3rd-Party Access, is where the contract lies between you and the supplier, such as the broadband or telephony company, but where an IT support company manages it on your behalf.
Managed IT services have their place and we can provide them. But we generally recommend the 3rd-Party Access model because it gives you greater control and transparency, plus it allows the most appropriate supplier and equipment for your individual needs to be used.
A managed services contract means committing yourself to one provider and there are likely to be a multitude of Service Level Agreements between them and their suppliers, any of which can affect your IT.