That heart rate sensor on the back of your Galaxy S8 can actually be useful for something
The way it works is simple: if the front camera has detected a face, tapping on the heart rate sensor will take a photo. Granted, there is a very obvious problem with using the sensor in this fashion: finger smudges on the rear camera. However, this is the very same issue as with the fingerprint sensor's placement, so if you've already formed a habit of regularly cleaning the lens, you should be good to go.
As it turns out, this is not a new feature at all – it actually debuted with the release of the Galaxy Note 4. However, it's now more useful than ever, seeing as the Galaxy S8+ is the company's biggest flagship so far, and thus may present grip problems for some people. So this can be a nice alternative for those who need it, but if the feature is not to your liking you can easily turn it off from the settings:
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