Harry could have been given a promotion just out of recognition of several years of competent service in an important bridge position. We're not talking anything senior here, just lieutenant jg, I think he was ready for that! Practically speaking it doesn't mean much more than a pat on the back and a "well done" but hey, he still deserves it and maybe it would give him a confidence boost. It would also mean he can't get bossed around by B'ellana or Tom, not that I ever recall them giving him orders anyway. As for miles, he's apparently the only NCO in starfleet so it's kind of hard to figure out how he fits in.