Every organization I worked for has benefited from a small file server to exchange documents and manage user accounts. You could rely on free cloud storage where the business consists of 2-3 people. However anything beyond that point would require a server in my personal opinion (especially within an office) – and it does not need to cost you an arm and a leg. Currently a brand new server with two hard drives and a UPS (protects from power spikes) should cost you below £500. You could purchase a pre-owned system from ebay (or specialist refurbisher) if you are on a tight budget.