You might want to let other family members in your household share your Core device with you. Or, you might just want to show it off to a friend and let them try a meditation for themselves. This is fine, but there are a few things you should remember.
The Core app learns about your typical heart rate patterns by studying your past meditation sessions. It uses this data to generate your personalized baselines, which it relies on to calculate your Calm and Focus in each session. If someone else completes a meditation while logged into your account, this may affect your baselines, and skew your future results.
This means that if you’re sharing your Core, the best thing to do is have the other personal create their own account, or to switch over to Shared Use Mode. Failing that, you can manually delete the results of their completed meditation from your History.
For more detailed information on how to do these things, take a look at this article.