Where a customer first buys matters a lot.
If a customer buys in-store while you were running a closeout sale, that's different than if they bought online during the same sale.
The sale probably attracted both customers, one to walk-in and one to click.
The in-person customer would had have to be physically in your store, would have interacted with your employees, would have seen the offers you have at the register, etc.
The web customer would have seen various offers, messages, and banners depending on their click path. They might have browsed or just focused on a single product.
This is their buying environment and context. It'll influence their later behavior and influence them in numerous ways. Even if they switch channels next time.
For example, that in-person customer will remember your employees when they are shopping online. They might search for that offer at your register. That sort of thing.
An optimized experience in one channel can then impact repeat purchases in another channel. A stellar employee can boost online store performance even if they never touch a computer. (And in reverse, a poor web experience can keep people from visiting your physical storefront). It's similar to the halo effect you might have heard about before.
That makes it important to look at the behavior of customers based on the sales channel they started with. Just measuring where an order comes from it not enough, you have to look at where a customer comes from.
Repeat Customer Insights handles this with its Acquisition Source tracking. It'll go through the order sequence for every customer to find out what channel they first ordered from and use that in many of its analyses.