Three Solutions to Win in Digital Marketing

Give people tools, not rules
Your people don't have time to endlessly ponder every post. So when it comes to tone, you need to find the sweet spot between too much guidance and not enough. A 57-page PDF of what to say/what not to say? Probably not going to happen. But equally, your brand values aren't a brief for writing. So by all means tell your people that you want them to be bold, but not arrogant; friendly, but not patronizing and so on. But don't expect them to have the faintest clue what that means when they start writing stuff for digital.
But do make it practical
That's why businesses are spending, on average, £116,000 on tone of voice. Because making it stick is just as important as coming up with the right tone in the first place. And that's when you start to see results. Like BT, who managed to save £6 million over five years. Sort your web copy and people are less likely to call you with questions. Deal with complaints well on Twitter, and you've saved yourself time and effort. That's probably why businesses who've done a tone of voice are more likely to want to use a specialist tone of voice agency if they're planning to do it again. (We would say that, wouldn't we? But that's what the research says.) We think that's because you get the most benefits from a tone of voice project when you roll it out with training and support.
You don't need a different tone for digital
Honestly, you don't. If you do tone of voice right, all your content should sound like they come from the same bunch of people. If you sound like a cheeky, irreverent scamp on Twitter and a regional bank manager from the 1970s in your customer letters, that's not helpful for anyone. So don't do that. If anything, it's likely your business is already doing some of its best writing on digital. So you might want to take a lead on tone of voice, and show other teams how it's done.