Not so much anymore, modern race grade brands like TEKNO don't require much shimming of their diffs, but it's good practice to check the shim on initial build just to be sure. Generally I rebuild a car after every 2-3 hours of combined run time, more info here:
Maintenance Tips
HoBao will...
There is no such thing as a "maintenance free" car, though I know many people will buy a RTR and bash it till it breaks, take it to their local hobby shop and have them make necessary repairs , rinse and repeat.
The risk with this philosophy is that you'll never know when a bearing has seized...