Aaron Dungca echoing David's notes — there's definitely a lot of nuance when it comes to how we might segment for a brand based on what they sell and ultimately the size of their business (and therefore list).
Big focus for us this year has been identifying clear splits between users that are likely to engage with a particular message and those that are not. Weeding out users that have not engaged with email content or otherwise on-site after being in the list XYZ time is something we pay very close attention to in terms of exclusions segments that we set.
Beyond that, we're super heavy on "likelihood of action" by leveraging information we have about that person's browse history, purchase history and provided product preferences to differentiate messaging to specific groups of users. For example, a client of ours sells movie posters. 100k+ SKUs across their storefront. A lot of opportunity to group users into various types of audiences based on what genres, films, franchises, actors, directors, etc. they have previously purchased and looked at and we also survey for genre preferences.
With that, where I could see Rebuy playing in is adding to that action-driven information. What products have been suggested to them in Smart Cart, what products have users added from Smart Cart, how are dynamic product recs being served, etc.