Leakage in Secure Two party Computation Am trying to understand Garbled Circuit based approach for Secure Two party Computation. There isn't much leakage in the classic millionaire's problem where the comparison circuit is used. 

But imagine they want to do some arithmetic operation (like addition or multiplication) without revealing their individual wealth.

Then although each of them need not reveal their individual wealth using Garbled Circuits approach (by running the protocol with an addition circuit),  the sum total of their wealth would easily reveal the other millionaire's wealth (By doing simple difference of the total wealth and self wealth)

So is secure two party computation recommended only for a class of circuits ?
Secure multiparty computation guarantees the nothing whatsoever is revealed by the process of computation. It does not say anything about the function. As you correctly point out, there are some functions that reveal a lot and shouldn't be computed, but this analysis is quite out of the scope of secure computation. The question of whether it's "recommended" depends on the application and the choices you may or may not have. You may, for example, want to use secure computation to compute a differentially private version of the function.