The Variant ID field is used to group child skus together. Retailers will want to use the same code/value on all skus you want to appear on the same PDP.
Example
Mens Sweatshirt
Available in Black and Gray
Sizes: S - XXL
*Brands will use the same Variant ID code for each of the size/color variants so that all will show up on the same PDP on live site.
Please be advised once a grouping has been published in the ShopSimon™ Portal, skus cannot be moved from one grouping to another. The only way to 'reorganize' sku groupings is to delete and reload the product data.
Please contact the ShopSimon™ Operations team at sellersupport@shopsimon.com for more information on this topic.