I think that the jury is still out on the true benefits to Guests.
We know that it was designed for Disney cash Guests and that the DVC using it has some limitations. We know that it was implemented to save Disney money and that they assign the rooms early and make up the room packets prior to the day that you check in. We also know that online room requests don't get passed to the room assigners. We know that the line at the Front Desk is often longer for online check in.
What we don't know is if it helps with getting your room requests, some people say that it does, others say that it doesn't. We also don't know for sure if it helps you get your room earlier.
Bill
My guess is that it would take the input of a CM with Front Desk experience to clear up the mystery. There's a lot of variables to room requests:
1 - Do online requests make it to room assigners?
2 - What rooms are available at the time of online request & assignment?
3 - What effect someone checking in the day before has on requests (ie does a walkup request on Friday trump an online request for Saturday)?
4 - If a better room opens up, who gets it? (my guess is walkups because it's too much work to redo everyone's assignments)
5 - What's the practice at that particular resort with those particular managers and CMs? As great as CMs are, they're human and we're all prone to laziness ... sometimes it's just easier to give the first room on the screen then deal with special requests. This is particularly true if things are really busy.
6 - How many "special" guests check in ... and by "special" I mean the ones who yell and scream and complain until they get what they want. You know, the ones that make us wish Maleficient would appear and deal with them personally

These "specials" not only take the preferred rooms from others who requested them, but they create a lot of stress and frustration amongst CMs and fellow guests. This creates a situation where special requests are less likely to be filled because the line is moving too slow.
7 - Maintenance, Mousekeeping, and late checkouts also have a huge effect on room availability.
All these variables can make it very hard to track how room requests are dealt with and without input from someone "in-the-know" I doubt we'll know for sure.