I find Marriott chat or message as it is called in the App, very useful for specific things Pre Arrival. I used it often for both early arrival and late arrival, as well as whether the property has knowledge to process Marriott GC as payment form. Occasionally I even asked for specific details of direction when google map is not clear on the final step(s) to get to the hotel. (can happen in international locations often).

For requesting items during the stay, I prefer using the phone "At Your Service" button or just the FD button - much quicker action than thru the chat which it is only attended to when someone is available to take care messages which remember, it is not only yours.