I think there are more advantages to being a former Governor than a sitting Governor running for President.
I think it depends on the state though. So much of modern fundraising is basically legalized bribery, with wealthy people donating lots of $ to politicians with power over their business interests. Because New York is a large state with lots of rich people, being the sitting governor of New York makes Cuomo an enormous fundraising draw. Even wealthy New Yorkers who don't actually like him or think he's going to win the presidency will donate $ to him in order to gain his loyalty, since his gubernatorial term would last another few years after the presidential race.
If he's no longer governor when he makes the presidential run though, then that won't work.
EDIT: Should note that all of the above depends on what New York's pay-to-play rules say. Apparently, there's a fair amount of variation from state to state. Depending on what the rules are in New York (and I don't know what they are) the ethics rules may make it tricky for Cuomo to raise huge sums from the financial industry while he's sitting governor.
That said, hasn't Cuomo managed to raise enormous sums of $ while governor? I assume he could do so again as a sitting governor running for president, but I think he'd struggle as a former governor. It's not like he's a hugely charismatic guy, nor does he appeal to some big underserved constituency in the Democratic primary electorate. If he's no longer governor, will anyone care enough about him anymore to donate money to him?
