Having a well defined value proposition [or værditilbud in Danish] is very important for every business, not least in BtC.
For all but the most known brands, having a value propostion that can be understood in a few seconds may be the differnece between a vistior staying on your site and a visitor leaving your site at once
conversionxl.com offers a great explanation including examples of good ones and bad ones
And to work with your own value proposition, you can use this template