A version set is a pre-built group of versions that you can apply to any mailing, so all the different versions you need are created automatically. This is particularly useful if you often use the same customer groups, product segments, languages etc. You can have different version sets for different customer groups or different teams. E.g. You might have one version set for a group of cities that you always send to and others for different age groups and product lines. Or you might have different sets for your regional or international teams.