It depends on what they're selling or what they're doing.
So, the thing that I always like to say is...
Take your top five to ten keywords and do a search for that keyword without a city name.
So just keyword phrase only no location modifier. If any of those keywords pull up a map pack, then that shows you that Google's using that localised algorithm and you should worry about local SEO.
If not the map pack, then the local algorithm doesn't apply to you and you don't really need to worry about it.
Now, if you're a nationally focused business, and you're wanting to show up in local like, an example of this would be Airbnb.
Airbnb serves customers Internationally, in lots of countries. They can't really set up an individual location for each property, so you kind of have to do a little bit of a hybrid approach where you're not doing anything related to Google My Business or actual location, but you're doing a lot of local content and localised optimization throughout the site to be able to show up there.
Answered by: Greg Gifford