Butter is as important for making pastry as flour is for bread. At Bourke Street Bakery we have always imported butter from Europe; first from Denmark and now from Belgium. We always use unsalted butter. There is no modern use for salted butter, as salt was only added to butter to prolong its shelf-life. These days most people have refrigerators so that is not a concern. Controlling the amount of salt in anything you cook is important.
Butter has different fat contents and different flavours but most importantly it has different roles depending on whether you are making croissants or other kinds of pastry. A pure and simple product like the croissant relies on good butter — without it, your croissant will be substandard. So, if you are making croissants at home, use good European butter.