Everybody knows the slogan of their favourite brand.
From Nike's 'Just do it', Loreal's 'Because I'm worth it' and Tesco's 'Every little helps' - most brands in the public eye have slogan. Yet slogans never change anything.
They don't grow market share or convince you to buy the product in the first place.
In between the lines of a slogan should be a story. And a slogan well told is a symptom of that story, a shadow of what you stand for. A slogan might be evidence that you have a story, but it isn’t a story. A story is something you live and connect with and come back again and again and again.
If the story of your brand is consistent, if it resonates with your audience and if you can defend it, then you're likely to succeed. And if your slogan reflects your story then it's worth having.
Apple has had various slogan through the years, but in every successful iteration of the company, the story has been remarkably consistent: Apple’s story is that they are idiosyncratic artisans producing beautiful products for smart people. That's not a slogan, but it's a useful tool for deciding if you're making something or doing something that you ought to be focusing on.
So by all means have a slogan. But don't bother wasting any time on it if you merely want it to be memorable.