Although Forrester analyst Sucharita Mulpuru said digital commerce is important year-round, there are a few factors that give it an extra boost over the holidays.  Read MoreHere's the bright spot in a tough retail quarter  For one, shoppers are more pressed for time during the Thanksgiving to Christmas period, which means they have less time to spend at the store, said Andres Mendoza-Pena, a principal at A.T. Kearney. If they do make it out, their overall experience is typically more hectic, including more crowded stores, fewer parking spaces and longer checkout times—not to mention the cold weather.  "The Web picks up quite a bit of share during Q4 because consumers realize it's easier," Mulpuru said, adding online sales penetration tends to pick up 2 or 3 percentage points during the quarter.  But it's not just convenience that pushes consumers from standing in line to clicking online. One of the biggest reasons consumers opt to buy in stores stems from their preference to touch, feel and try on items. But because much of the spending over the holidays relates to buying gifts for others, this hands-on interaction isn't as important, Mendoza-Pena said.  Gifting's impact becomes even more important over the holidays because as more Americans receive smartphones, tablets and laptops, their penetration becomes even more prevalent, Mulpuru said.  "There are a lot of people that get phones and tablets during the [holidays] and then use their devices to do everything, including shop," she said.  The demographics tied to back-to-school shopping also put it at a natural disadvantage for mobile usage. According to a recent study by Kearney, millennials have the highest preference for using a combination of e-commerce and in-store shopping. But both Gen-Xers and teens, two groups with a higher influence on back-to-school spending, showed a higher preference for in-store shopping.  "Shopping malls are extremely attractive to [teens]," Mendoza-Pena said, adding that the group views them as a way to socialize.
Despite the growing importance of e-commerce, digital sales will likely play a larger role over the holiday season than back-to-school.