I have tons of fun coming up with names for NPCs, and to lend some credence to my own campaign world I've done work on several of the royal lineages of different companies. Beyond simply knowing who ruled when, it helps to give a generational sense to a country's history. For example, imagine what happens when a tyrannical, war-crazed despot dies and leaves the kingdom to the heir he never entrusted to lead his armies - or was so paranoid, never had an appointed heir?
At the same time, you may do yourself a disservice by mapping lineages too closely; it is all too easy to write yourself storywise into a box. Do a couple lineages for fun and practice, and then just fill out others as needed for a story, and then only as far back as you need.
As an example: I ran a campaign that started in a small town known as Edgeridge, a few miles from the Thunder Mountains in Klinn. The two most well-known families were the Tarascon and the Narnsons. The Tarascons used to work as caravan guards for the Narnsons, but over time decided to go into the trading business themselves. A couple of generations back, the Narnsons had a trading manor/warehouse/fort near the opening of a pass in the Thunder Mountains. It was overrun by goblins and the Narnsons blamed the Tarascon for the loss (convinced the Tarascon had purposely understaffed the fortress with guards so it would be easily taken and the Tarascon left as the only merchant family). It set up things for a Romeo/Juliet sort of house rivalry into which I could thrust the characters - one of the first adventures the party went on was to clear out the old Narnson fortress and scavenge whatever goods they could to return to the Narnsons in return for future equipment discounts. On the other side, the Tarascons could provide combat training and "guard" missions, so the players had to learn and played both sides to their advantage. The intra-NPC relationships also had many interesting side effects as other NPCs in the town had their lives and interactions with the PCs influenced by association with the two families.