Some years ago now, HMRC surprised everyone by quantifying the level at which they considered a non-cash benefit given to an employee to be trivial and disregarded for tax purposes. £50 was much higher than everyone had imagined up to that point.
It doesn't represent carte blanche to give people an onslaught of things worth £50 in lieu of taxable pay! If the provision of benefits becomes regular enough that it's effectively become just part of the deal with the employee and therefore contractual, it'd just be taxable as normal. So a £50 John Lewis voucher every Friday or every month isn't going to work. But sporadic £50 vouchers are fine.
The rules are tighter for directors - there's also a tax year cap of £300. But that's still six £50 vouchers! Or, if you're particularly prone to getting the wrong card out of your wallet and accidentally using the company one from time to time, the trivial benefits allowance can be used as a backstop so that you don't have to repay the company when that happens.
A small win perhaps, but small wins at the expense of HMRC can be disproportionately satisfying!