Or a purpose, for that matter. Both are meant to show what an organisation really stands for - and what it stands against. They should make priorities clear. Their value (forgive the pun) is in showing the way through difficulties. They're meant to make "the right thing" obvious.
Sadly (and inevitably) too many businesses are making something else obvious. It's really all about the money, until pressure gets so intense that they'll rustle up some principles.
Look at how some of the world's major corporations have acted over Russia's invasion of Ukraine. Should anyone be supporting that régime? That should be a no-brainer. Especially for any business that, for example, wants to "nurture the human spirit" or "refresh the world and make a difference" (does anybody understand what either of those vacuous statements could possibly mean?) and let's not even go near those who want to make "delicious feel-good moments easy for everyone".
Huge professional services firms have been tying themselves in knots, looking for ways out of their own moral dilemmas. Keep quiet? Accept no new mandates? Find a different corporate structure? You tell me how a sector which includes 'purpose' ideas such as "driving progress" and "making business better for everyone" can possibly struggle to know what the right thing to do is.
You have two options: either take your purpose and values seriously enough to define them well, test them rigorously and live by them without exception (don't, in that case, be the law firm that has declared its purpose as "building the next generation law firm"). Or don't bother. Just say it really is all about the money. There's nothing wrong with honesty (it's served Ryanair very well so far).
Just remember: "Integrity means doing the right thing, even when nobody's watching".