My view is that multiclassing penalties are not needed.
The only argument for this type of penalty that I'm aware of is that one should punish people from 'dipping' too much - however, I think this is flawed:
- They do not help balance as multiclassing builds are still possible, just more annoying to level
- The distinction between PRC and base class is often arbitrary (eg say a fighter decides to take rogue, he gets a penalty, while someone taking assassin does not - yet rogue and assassin are quite similar)
- Many base classes are much more similar than base class + PRC combinations, making it difficult to justify why the former should be penalised (eg a barbarian / fighter seems more 'coherent' from an RP standpoint than a barbarian / anointed knight)
- If one wanted to simply punish dips, then the penalty should only apply to 3-4 class levels (ie so if taking 20 barbarian / 10 fighter there should be no penality, but for a 27 barbarian / 3 fighter, maybe)
What are your thoughts on the topic?