I don't actually study the Principate, but the province of Egypt was not a "real" province at all. During the Principate provinces were divided into Imperial and Senatorial provinces--the Imperial provinces were usually the ones that had legions stationed in them (with the exception of Africa, the only Senatorial province with a legion), or the wealthier provinces. Imperial provinces had their governors appointed by the emperor, but the governors of the Imperial provinces were still senatorially-appointed magistrates (holding the minor office of legate) and were granted by the senate promagisterial powers, technically making them promagistrates will still serving as legates. Egypt's administration was completely different--it was the only province that could only be governed by a man of equestrian rank (i.e. not a member of the senate--an equestrian isn't actually just a rich plebeian, it has the particular nuance in Latin usage that an equestrian family is a rich plebeian family with no political standing. In other words, a rich plebeian family without anybody in the senate or holding a senatorial magistracy). Egypt was governed by an equestrian prefect appointed directly by the emperor. This wasn't all that odd, as many provinces were governed by equestrians (most provinces could fall to men of any class), but equestrian prefects were of pretty low standing and were pretty much totally dependent on the emperor. Nor could the senate legally interfere with the appointment or actions of equestrian prefects, unlike with the provincial legates, who had to be approved by a meeting of the senate, at least technically. So Egypt was more like an imperial prefecture than a full-blown province, at least in the way it legally was treated. The other thing is something that Tacitus mentions--the emperor had total control over what went in and out of Egypt, which was not true of the other provinces, Imperial or Senatorial. Travel between provinces was totally free for everyone, except with respect to Egypt. Tacitus says that senators and equestrians had to get permission from the emperor to enter Egypt legally. Other than that I'm afraid I can't say--like I said, I study the end of the Republic, not the Principate. I also don't know much about economics--which sucks, because I've never looked up the tax collection of Egypt, whether the funds collected in the province went into the treasury or the emperor's private fortune