Have you ever heard the phrase “One stop shopping?”
I have heard that phrase in large and small companies with regard to Information Technology. The reasoning is usually that one vendor for all their IT needs will avoid finger pointing and minimize the risk of mismatching technologies and many more reasons.
I would say that if a company already has strong leadership in IT and already has a significant investment in one vendor, it may be the best choice.
However, if your company does not have strong leadership in IT and / or you don’t have Enterprise Architecture and processes in place, it may NOT be the best thing to get your full IT solutions from one vendor.
The reason you shouldn’t is simple, don’t seek leadership advice from a vendor that will supply all your hardware and software and services. Their Enterprise Architect will only give you advice that leads to the products and services his company offers.
My recommendation is to have your IT leadership either Internal or to outsource that to a consultancy without ties to any one vendor. That will allow free thinking and optimal results. You may still end up with a single vendor for hardware and software, but it may be more likely to have a solution stack that is both compatible and cost effective. Most importantly you will get a long term Enterprise Architecture that will be agile, performant, and reliable.