There is a wide variation in how properties process advance check in on the app. Some properties allocate a room immediately (or at least before my anticipated arrival time) and I just pick up my room key when I arrive. Others they still assign the room when I arrive and I may still have to present my credit card. I am seeing more of the latter recently. Going back a few years, there was a property I stayed at fairly regularly in Philly. Most of the time I got an upgrade to a suite. If it was an especially busy week it might just be a better regular room (high floor with a view). The results were the same regardless of if I had checked in on the app. or not. Distilling it down I don't think checking in on the app. has any impact on your chances of getting upgrade. Well managed properties will pre-allocate rooms and give upgrades based on their criteria before guests arrive for the day. Less well managed properties will do it on the fly as guests arrive. For all of the above, nothing prevents you from asking for an upgrade when you arrive if you haven't already been given one.

As a different poster already noted, asking a day or so before you arrive is the best way to try to get an upgrade. Finally, the FT maxim applies. Book the room you will be happy with. Don't depend on an upgrade to get it.

--Jon