This shouldn’t come as a surprise to anyone who has read the EULA for Tableau (you did read it, right?), but to help some people out I thought I would point to this helpful FAQ on their website about licensing and the number of installations:
Basically, for each desktop license purchased, an authorized user can install Tableau on 2 machines, a primary and secondary computer. It is assumed that the primary machine is a desktop at work. The secondary machine is either a laptop or home computer.
NOTE: This information is accurate as of the date I’m posting this, but their EULA could change. Be sure to check the current version to find out where things stand. Information on licensing and installation is in section 2.2 as of this post.