Well I was told by a few people that I'd need such an account. I guess they're mistaken?
I've also thought that this would be very inconvenient if it was the case.
Multi-currency accounts are not common and not offered by all banks.
If you don't need to receive funds in currencies different from the one thay you use daily, than yes the few people were mistaken.
A multi-currency account would make sense if you are operating on the stock market. You could keep balances - for instance - in EUR, GPB, and USD and operate at the same time on any stock exchange operating in EUR, on the London Stock Exchange and on the NYSE/NASDAQ.
This would greatly reduce profit erosion because you would eliminate the conversions needed if the account was "single currency" (you would fund the trading platform, usually offered by the bank, without worrying about conversions).
I hope all of this makes sense to you.