For example, in Skyrim, it makes the most poetic sense for the Dovahkiin to be a human: he fights the Thalmor, goes to Sovngarde, carries the title held by so many human Emperors, etc. There's nothing to keep someone from being an Altmer or Dunmer, but being a man, using the thu'um and walking in the steps of Talos just seems right.
I'm going to be starting Morroblivion (a port of the entirety of Morrowind into Oblivion that allows for beefier graphics/gameplay) soon. I'm still conflicted on what my race should be! Shall I choose a Dunmer and truly be Lord Nerevar (yes, I know he was Chimer) reborn? Should I be a Breton or Imperial, owing my allegiance to the Emperor and fulfilling the prophecy to serve the Empire and discover my destiny? Or should I be an Argonian in an ironic twist of fate, and become a hero of Morrowind, despite the debasemant of my people? I'm looking to you, Lore Buffs, to help me decide.