Tl;dr - I refer the reader to Betteridge's law of headlines.
But if you have a few moments spare in your busy day, the answer in most cases is the same, however there's a more nuanced argument to the question than just a single word.
It's a question I've seen many times in LocalGovDigital circles, and since it came up again in the Slack group recently I thought it might be helpful to put my answer to the person asking the question there in the form of a post for a wider audience.
So the first and foremost question for any council considering building an app might be what is the established clear user need for an app that a good mobile-first website can't provide?
And by 'established clear user need', I don't mean "as a civically-engaged citizen, I need to tell the council about a pothole or some flytipping I've just seen whilst out and about, so that I can drive safely along that road next week". The question is, is there a clear user need for an app which a user will download to their phone (and remember on which screen or folder the icon for the app is kept) which you can reasonably predict the users will use at least once a week because the functionality you're hoping to offer is something tending towards the specific that an individual user needs to do regularly and thus an app will make it easier for them to do that thing, or is the idea more to replicate some of the general services available on the website? If the former, then yep, there's a chance an app might have legs, but if the latter then the question is returned to of what's the established problem with the mobile view of the website for which an app is thought to be the solution.
So you've got this far and still want to investigate further - do you have the talent in an in-house team to create, and more importantly maintain, an app, or are you going to commission an external agency to do it for you? Do you have publisher's accounts with the two major app stores?
So you've deployed the app, what next? Whilst a website CMS you can just put it live and leave it on that version of the software (although that's not recommended!), you can't do that with an app deployed to the app stores - even if you don't actually update the app itself, the frameworks that most apps are built up get updated regularly, and whilst a website on your own server with code you've paid for, the vendor can't force you to do updates, the app stores hold all the cards, and they set an expectation that the frameworks they allow to be published in the app store have to be within so many versions, and thus apps built on them have to be kept updated accordingly - and if you don't keep the app's frameworks updated, then the app store will pull your app.
Now there is useful functionality that can be developed in apps which can't readily be developed for a mobile website - there's a personal project I'm working on which is marginally compromised by restrictions iOS places on system access via a web page that it doesn't place on a native app - and if you know that the service you want to apperalise will generate repeat business from individual citizens and it's making use of that native functionality, then by all means app away.
But the default position for any any consideration of apps for citizen LocalGov purposes should still be framed in the language of 'here's a problem, can it be most effectively solved using an app' rather than 'we want to have an app, what can we use an app for'.