I sort of waffle between having a complex background, to a tabla rosa background, and let the game change my PC, in both instances.
The complex background can offer an interesting twist to my PC's reactions -- I know how I, the Player, might respond, but it forces me to think "How would the PC respond?" Which can be challenging, and sometimes more stimulating. I find this to be especially true when i'm playing other races, especially city elves.
The tabla rosa background can offer a more 'in the moment' sort of gameplay for me. I have to pay closer attention to what's going on around my PC, and shape the PC to those events, rather than have them exclusively 'react'. As there aren't as many past incidents to compare to and think "How would the PC react?" I find myself reacting more as how I, the player, would react, and it can actually feel more immersive in a Virtual Reality sense.
As with most things, there's a middle way between the two extremes.