I think anyone that is even a little bit serious about their particular exercise/activity will not use this. I cycle and run. I record everything in Strava. Most of my friends do too. I can't really see a reason to use this. Counting steps does not seem to be very useful.
The data from Strava will sync into Google Fit (if you want), then if you wanted to switch to a new app in the future, it could bring in your existing data from Google Fit. Essentially this can act as an external datastore for those apps, rather than your data being locked into Strava's infrastructure.
It's hard to think of this as useful with Strava as it's so damn good, but there are many other apps for other activities that are not as nice to use, but users are locked into them as losing all your data means starting with a new app is frustrating.
