You are right in thinking that OSV is a construction that changes the emphasis of the sentence. To demonstrate:
1: Do you like pasta?
2: Not really.
1: How about pizza?
2: Now that I like!
This is a feature of language called "Topic-fronting" that can occur in many languages. As you can see from the example the focus of the sentence is moved to the object "that". In this case, it also stresses that the response is different from the one that preceded it. In English, it's often used this way e.g
I despise most German composers, but Mozart I like!
I'll also add that the usage of OSV in English is mostly idiomatic. Limited to certain contexts and can come across as strange if overused in ordinary language. The most common context in which I see it used are contexts in which it might be appropriate to say something like "Now you're talking!". It carries a connotation of slight oratorical flair that might not be appropriate for, say, a dreary business meeting.
I should add that your example:
Making excuses for lying politicians does not an honest man make.
Is not an example of OSV topic fronting at all. In fact, what you've got is SVOS. Your sentence has two verbs. So perhaps a different example might be in order.
Making excuses makes an honest man.
This example is simply the standard SVO. Compare:
Making excuses an honest man makes.
This is a clear example of SOV, however, I doubt it would occur anywhere asides deliberately poetic or archaic-sounding language. On the other hand, the expression:
X does not a Y make.
Is also very idiomatic in English, and its use is almost exclusively restricted to sentences involving the verbs "to do" and "to make" plus a negation, although other verbs are possible. In many ways, the SOV formation is the very opposite of OSV, as it draws attention away from the object and places it on the verb. However, similarly, SOV is sometimes used to draw attention to the fact that what was said previously is now being contradicted. e.g
1: The expensive school my children attend should ensure they grow up to be gentlemen.
2: Expensive schools do not a gentleman make.
As before, I'd be wary of overusing these phrases if you're not a native speaker. They're highly situational, and if you overuse them you risk sounding pretentious.