There are different reasons why people want to combine New Zealand's two most popular peaks - Mt Cook (NZ's highest) and Mt Aspiring (arguably one of the most aesthetic) into one trip. For some, New Zealand is a once in a lifetime experience and since they have come all this way they might as well make the most of it.
For people new to New Zealand climbing, it is the perfect way to get to know the country and its many faces. The mountains, flora and fauna vary quickly in New Zealand and combining a climb of Mt Cook & Mt Aspiring lets climbers experience the lush temperate rain forest of Aspiring National Park as well as the deep glacier carved valleys of Mt Cook National Park.
Other people appreciate the chance to get in a major climb of a peak like Mt Aspiring with their guide before tackling Mount Cook. It is a chance for you and your guide to get to know each other and work on systems in a more forgiving environment before moving on to the more objectively dangerous slopes of Mt Cook.
Some people are unsure if their experience is enough for Mt Cook and use Mt Aspiring as a prerequisite. The guide can get a clear view of the client's abilities and give advice on whether Mt Cook is a realistic option. If in the end it is felt that Mt Cook is not a good idea there are many other great climbing objectives to tackle.
What ever the reason, if you love mountains, this will be a beautiful romance.