I've used TP several times. I have also made requests via Chat. Both are, as I would expect, hit or miss.
several years ago through the member publications, they told us to NOT send faxes or emails to the resort room assigners, and that they would be ignored. Inquiring minds want to know why that has changed,
I suspect this is just a by-product of The Way Disney Does Things.
The general guest services playbook at Disney World is: Never say no to a guest unless you absolutely have to. One reason you have to: It costs too much staff time/money/whatever to deal with the request flow. Another reason: It is impossible for everyone to be on the first Space Mountain rocket of the day.
Back in the dim history of time, it had gotten to the point where it was just common knowledge that you could fax requests in to the resort. But, that creates a ton of work for the back-of-house folks. Perhaps more importantly, most people are requesting the same small number of "best rooms," and despite the fact that requests are not guarantees, making the request often puts the expectation in the guest's mind that the request will be satisfied. If everyone is asking for the same few rooms ("overlooking the Village Green" for example) then most of those people are disappointed. To paraphrase Homey D. Clown: "Disney don't play let's disappoint the guest."
So, the word went out: don't fax us, and we will ignore it if you do. That removes the problem of unsatisfiable expectations, because there can be no expectations.
And for a while that was the rule of the day. Inevitably, as turnover happens, management forgets what the cluster-buss of Everyone Faxing looked like, and starts considering requests again, because We Don't Want To Say No. I have no idea how those requests are taken---presumably, they are not still using a fax number, but who knows? There are several ways to make such a request: You can call or chat with Member Services, or you can use TP's form. I don't have the sense that any one option is better than the other.
If things get to the point where either (a) it is a ton of work to deal with them or (b) guests start expressing unmet-expectation disappointment in noticeable numbers, then we will probably go back to: "Use the drop down requests, nothing else." I don't think (a) is likely to happen, because I vaguely recall that WDW has automated quite a bit of the back-of-house work, including first-cut room assignments. However, I will not be surprised if (b) happens, because people can be possessively ornery about rooms.