Making the manifest shouldn't take much time so it should be harmless, if nothing else, but I wonder if it's worth advertising via a banner or investing in deeper PWA features like offline availability.
So from a business perspective: if you have a PWA, do people bother installing it? Particularly when you also have a native mobile app. Is it worth spending effort on?
We’ve found trying to drive home screen installs to be generally useless. But announcing new mobile web app features through the usual channels (“what’s new” monthly emails etc) does seem to affect usage.