The most profitable customer is a "multichannel customer": a customer who engages with you across your various touchpoints.
eCommerce does not and will never cannibalise physical retail sales. In fact it enhances and grows sales in-store.
Studies have proven, consumers who do not purchase online, research online before they go into a store to purchase.
Omnichannel retailing builds customer loyalty. Studies have proven customers are less likely to leave a retailer if he/she engages with 2 or more of your touchpoints.
Why?
If a consumer has a bad experience and only interacts with a single touchpoint, the consumer assumes this one bad experience will most likely occur across the other touchpoints.
However, if a customer engages with multiple touchpoints from your business, and has a bad experience from one touchpoint, they assume its a one-off because they have had good experiences from the other touchpoint(s).
The proof in the power of a omnichannel strategy can be seen with large online-only retailers moving into physical bricks and mortar: Casper, Warby Parker.