Omni-channel services such as "buy online, pick up in-store" are helping retailers cut costs and boost sales, executives told CNBC.

Lululemon Athletica says its online sales grew by 35 percent year on year this past quarter, in part because 150 of its roughly 440 stores now offer buy online, pick up in-store service.

Similarly, Target says its Shipt same-day delivery service for curbside and in-store pickup drove more than half its e-commerce sales growth of 42 percent for the quarter, as well as 25 percent of same-store sales growth.

“On any given day, upwards of 50 percent of our orders are delivered next-day, and it’s using our stores and their proximity as that advantage in our overall strategy,” Target CEO Brian Cornell said in a published statement. “We’re leveraging the fact that we’re so, so close to the guest … and convenience is a big part of our strategy.”