"First and foremost it gives us scale. We have invested a lot of money over our 10 years in the efficiency of our business.
"We have built a whole bunch of tools and technologies and having a much bigger book to spread the cost of those across really gives you the economies of scale."
Ballantyne said BNZ's life insurance book was older and already cashflow positive which balanced out its newer policy book.
"Which means we will be able to list, if we want to list, sooner because that dividend story will happen sooner than it otherwise would."
Ballantyne founded Partners Life in 2011 and it currently insures more than 177,000 lives, has $343.3 million in annual premiums in force and employs 270 staff.
"The trouble with growing as fast as we have is you are always sucking in capital not spitting it out because new business proportion to your existing book never quite catches up.
"So that is why something like this with an in force book makes a significant difference."
Ballantyne said in order for an IPO to go ahead the markets had to be right and the regulations for the sector settled for potential investors to understand what they were investing in.
"Much as we would like to have already been there it is good we don't have to be there that we have got shareholders that have been patient and happy to invest more capital into business as we have needed it."
Its largest shareholder is US-based private equity giant Blackstone which has a 49.8 per cent stake in the company. Partners Group Nominees owns 23 per cent while Maui Capital Aqua Fund is the third largest shareholder at 9.7 per cent.
BNZ's life insurance book has 102,000 policies and its 116 staff would be offered the chance to move to Partners Life once the deal was finalised, Ballantyne said.
She said the BNZ customers would be moved on to Partner's Life's systems within a year of the deal being finalised - expected to be by the end of 2021.
As Partners Life was buying the BNZ business it would not pose any problems for underwriting the new customers.
"We are buying all the risks and liabilities as well as all premiums so those customers are completely covered - there is zero risk to their cover as part of this transaction."
In a statement to the New Zealand stock exchange, BNZ parent National Australia Bank said the agreement to sell the business was consistent with its strategy to focus on its core banking businesses across Australia and New Zealand.
BNZ chief executive Angela Mentis said the bank was confident the sale would provide the best outcome for its insurance customers.
"Ensuring BNZ customers continue to access insurance remains important to us. We're confident that this sale will provide the best outcome for our insurance customers and that they will continue to receive a high standard of customer service from a New
Zealand insurance provider with a strong local reputation."
As part of the deal, BNZ has also entered into a 10-year exclusive referral arrangement with Partners Life subject to Partners Life continuing to meet certain operating standards.
Ballantyne said her team were probably too tired to celebrate the deal which had been months in the making right now but would probably do something after Christmas.
"They are all exhausted. None of us want to drink or eat anything. But after Christmas I'm sure we will."
She said the deal meant the business could end the year on a high note.
"It's been scary, more scary than tough I think because you just didn't know what tomorrow would bring and what that would mean to staff.
"But we have got to the end of the year and it is feeling much more comfortable now and now there is a vaccine and to have this news as well for our staff. I think it was a very well received piece of news."
