In every hotel I've worked, the property management system (PMS) is programmed to assign the least-used room in the category during the check-in process. This procedure is an attempt to keep the "wear and tear" roughly equal for all rooms. After all, no GM wants to spend money renovating all rooms when only 75% need it.

While it's a sound principle, the reality is that for many hotels, rooms within a single category are not the same. There generally is a good reason why most Front Desk reps ignore the auto-selected room. (Example: next to the elevators or ice machines, no view, odd layouts in older buildings, etc.) Therefore, a completely automated check-in process will be more likely to assign a less desirable room since the software doesn't differentiate any differences within a room category.

Caveat: I've never worked at a Marriott hotel. Perhaps someone who has can provide a more informed opinion on this matter with regard to their brands.