The downside was that it also provided certainty for the Opposition.
The power to set the election date gave the governing party quite an advantage. It meant you could revise and rush to the polls earlier if the polling looked right.
It also meant you could plan ahead and shovel bucket-loads of taxpayer-funded advertising material at the voters, closing the tap off when the regulated period began.
Your rivals had to be more careful because they didn't know when the regulated period began - the period during which stricter rules and spending limits apply to advertising.
Not only could they have inadvertently broken Parliament's rules, but they could also have to sacrifice great reams of campaign advertising to avoid blowing the spending cap.
Former Prime Minister Helen Clark usually gave two months' notice of the election date. The regulated period was three months (except in 2008 when it was for the entire year up until election day.)
Key merrily gave away that advantage. That is to his credit.
Working out an election date is a complex formula, involving scientific calculations of the weather, All Blacks fixtures, important international summits, public holidays and school terms as well as what the polls might do over a year.
Key would announce the election date in February - six months before the election. It is still not required in law but Key has set a precedent it will be hard for any future PM to go back on.
Unsurprisingly, Labour in Opposition now backs Key's approach of an early call.
English has made it clear he will follow Key's lead, saying he expected to announce the day in short order.
English has declined to follow Key's lead on another matter: that of sucking up to the President of the United States.
Key charmed and elbowed his way into former US President Barack Obama's peripheral vision very soon after both became leaders. He has left Trump for English to deal with.
English has basically already thrown in the towel. If Key was the squeaky wheel seeking oil, English is the ostrich. He is staying quiet and hoping Trump does not notice him.
Key's slogan was "ambitious for New Zealand". It meant that whatever headwinds assailed him, Key would smile and put an optimistic gloss on the chances of getting something done.
Had the US pulled out of the TPP on his watch, Key would have talked up the chances of a bilateral free trade agreement with the US and salvaging the remnants of the TPP.
In light of Trump, such assurances would have been easily recognisable as "alternative facts".
So English didn't bother. He simply said New Zealand would be at the back of the queue for the US and he probably wouldn't want a free trade agreement on Trump's "America First" terms anyway.
English is not one to waste ambition on lost causes.
