Licence and number of controlling kernels

I'm trying to understand the differences between controlling kernels and subkernels.

I created 3 local kernels (kernel configuration options > add), each using a maximum of 8 local subkernels.

Controlling 2
Computing 8


So what are these "controlling kernels" ? Is there a limit on local kernels that can be started ?

Cf. This question on the same topic, but the answers appear contradictory. Following one of these answers, I don't understood how I am allowed to run 3 local kernels.

Additionally, what is the difference between launching 1 front-end and having many local kernels and launching many front-ends each with only one local kernel ?

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Do you actually get to run 3 master kernels in parallel? Creating new kernel definitions is not equivalent to actually running them (see also: reference.wolfram.com/mathematica/tutorial/WhatIsMathLM.html) –  Yves Klett Jul 5 '13 at 7:58
I just noticed something funny: I have the same licensing as the OP. I create a third kernel definition and open three notebooks. If I try to select the three different kernels as the notebooks' kernels, I just can't! The frontend won't let me do that, but switch around the settings such that only two different kernel definitions are selected at the same time. Very sneaky :) –  sebhofer Jul 5 '13 at 8:41
@YvesKlett I indeed created 3 local kernel definitions (+ remote ones), I opened three notebooks, pointed each one to a different local kernel and executed Pause[10] on each of them simultaneously. –  Cedric H. Jul 5 '13 at 22:11
@sebhofer It seems that I don't have the same behavior (see other comment), could you give more details on what s happening for you ? –  Cedric H. Jul 5 '13 at 22:12
What exactly is your license setup like? You mention remote kernels, too. –  Yves Klett Jul 6 '13 at 7:31