I agree with J.D. that it isn't meant to be a punishment. Tough love may have some use where it's a matter of letting a person suffer the natural consequence of his or her own actions. If someone bails us out every time we do something dumb, we're less likely to learn from our mistakes. Or at least that's the theory.

It can't make a sick person well, but it may help convince a someone to seek out and take treatment. So if I'm bipolar, and I've done things while in a manic state - destroyed relationship, run up huge bills, etc. - that make me suffer once the mania is past, I might eventually be motivated to try and avoid being manic again. If someone else cleans up after me, though, I don't have that motivation. So it won't directly cure someone, but it might help them seek help.

Personally I think tough love is a bit harsh. There has to be genuine compassion for the suffering of the person.