Sometimes, the Emperor plants a Noble on a planet because it's cheaper than sending a flag all the way from Capital. The Noble is already there.
Sure, but the noble doesn't govern anything or actually have a job resulting from the title.
William the Conqueror, Duke of Normandy, actually governed the province of Normandy and had vassals delegated to governing portions of it. That's the medieval version. Works great for a fantasy campaign. This isn't a fantasy campaign.
Arthur Wellesley, Duke of Wellington, did not govern anything (except when he was elected Prime Minister). The "Duchy of Wellington" is house his family already owned in the town of Wellington. (Technically, his brother bought it so they could name the Ducal title that was about to be created for Arthur after the town, because he liked how close the name was to the family's name.)
I tend to think the latter model is how it works in Traveller.
Emperor: "Woah, good job defeating those Vargr corsair fleets with that ragtag collection of armed freighters you gathered up. Imma gonna make you a Baron. Whatcha wanna be the Baron of?"
New Baron: "Well, I grew up on Crabtree Lane. How about Baron of Crabtree?"
Emperor: "Done!"
The Baron of Crabtree doesn't have any authority in Crabtree. He may not ever even go there. It need not even be an actual location. He gets to vote in the Moots he belongs to, though. Or, more likely, he can trade his proxy for favors or remuneration to someone who does bother to hang out where the Moot meets. And he may get an imperial stipend (aka fief). Which could be in the form of real estate, but probably isn't. Because the Imperium's assets are primarily in trade revenues, not in real estate portfolios.
IMHO.