There are definite benefits in allowing a One No-Trump opening to include a 5-card major. More and more experts at international level have adopted such a style.
If you are an ambitious player and are keen to improve the range of your no-trump bidding you will need a method to locate a 5-card major with opener or to discover a 4-4 major fit.
5-Card Major Stayman provides an easy structure that allows you to do just that and still enables you to use transfers to either major, even after a INT:2C response.