I see this on other websites also, not just Marriott -- Google search suggests various possibilities, like inferring whether you're sitting/lying down etc., that this data can be used to "fingerprint" a person without using cookies based on how they typically hold their phone, detecting human vs. bot, etc. Most of the legitimate applications seem more suited for mobile apps rather than websites (e.g. taking action based on the shake gesture, am I currently driving, etc.)

I have it blocked by default for all sites in Chrome and haven't noticed it impacting any website functionality /shrug