Most UK business accounts hold only GBP. When you receive a EUR payment, the bank converts it immediately — at their rate, with their margin. You don't get to choose when or how to convert.
A multi-currency account works differently. Your EUR invoice gets paid into your EUR IBAN. The money stays in EUR until you decide what to do with it — convert it, pay a EUR supplier, or just hold it. You're in control.
For businesses working across borders, this is not a nice-to-have. It's how you stop giving money away on every international transaction.