After reading documents and learning, it is about time to buy the license, but not very sure the limitation.
I have 3 computers, one at office (mac mini), one at home (imac) and a laptop (MBPR) to bring everywhere, if I buy the pro license, can I install on all 3 of my computers?
Yes you can. If you want to install on a fourth computer, you have to release the license from on the the already licensed ones.
You can install and develop with fourth computer but You cannot build with it.
You only need license to computer You build with.
Oh, I understand, I can build apps in only 3 computers, the others I can still install but can not build.
Plus you can disallow the license on a computer and activated it on another from your online account in a couple minutes.