Jetblue seems born to be a cloud marketer.

The airline is digitally savvy, maintaining an active Twitter feed and customer-friendly website. Running its entire enterprise-marketing operation -- from email to analytics -- on software accessible anywhere with a web connection looks like it would be a natural fit.

But JetBlue only made its first significant jump into the cloud last spring when it signed on with Oracle's Responsys, a marketing-automation tool.

"We're definitely in the experimental phase at this point," said JetBlue Digital Commerce Head Maryssa Miller of the company's foray into the cloud, which included putting its email marketing there.

Cloud-based software presents marketers with some advantages: It's widely considered more powerful, accessible and better-connected than on-premises software. But when it comes to putting everything in the cloud -- email, content marketing, data management and analytics -- most marketers are like JetBlue, carefully choosing what can be kept off-site and what functions needs to stay at home.

There's no simple answer about the right mix, but there are a number of factors to consider.

Why on-premises live on
There are reasons on-premises marketing software still exists, beginning with the fact that migrating to the cloud is a serious commitment. "If [marketers] are doing just fine and getting what they need out of an on-premises solution, then there's no incentive to change," Forrester analyst Cory Munchbach said. In some cases, the effort can require moving tens of millions of customer records, she said. The cost and time will be dependent upon the complexity of the records.

Some simply feel safer keeping their customer data on their own servers. "The perceived reputation is that on-premises is more secure," said Ms. Munchbach. Marketers may have access to customers' email, credit-card information and even more-intimate data from wearable devices, she said. It takes trust to leave security in the hands of others.

Cloud companies have been battling that fear for years and insist they've got things under control. "Data security is core to the existence of cloud-software companies, which is not the case for most marketing organizations," said Bryan Wiener, chairman of enterprise content-marketing software company Expion. He declined to comment on Expion's security practices.

Andy Markowitz, GE's director-global digital strategy, said his company is careful about what information it puts in the cloud, "but we are so not far from a point where everything will be in the cloud."

The case for the cloud
Pushing activities to the cloud can pay serious dividends for marketers. Many interact with customers on the web, through email, on social media and mobile devices. And there's often a software app to manage each type of interaction.

Adobe, for instance, offers different products for web management, social marketing and analytics. Syncing these programs can give marketers a "unified customer profile," allowing them to coordinate messaging. Cloud-marketing software can quickly integrate and pass data back and forth. "All your information can be accessed in one place," said Ms. Miller. Before it migrated to the cloud, she said, "JetBlue sometimes had little visibility."

Cloud software also has practical advantages: Updates can be deployed automatically; software can be purchased a la carte; and the cost is often cheaper.

"Marketing toolsets -- especially those that are interacting with digital channels anyway -- make great sense to be cloud-based," said Mark Yolton, Cisco VP-digital strategy and enablement.

If a company's workforce spends a lot of time on the road, cloud software can be accessed anywhere. "I can't even imagine how I would monitor my campaigns if I had to query on-premises databases," said Salesforce Marketing Cloud CMO Michael Lazerow. "Who wants to be fidgeting with a VPN and a WAN and a LAN and a SAN just to get access to some reporting that's going to drive a decision?"

Not either/or
Kevin Akeroyd, general manager of Oracle Marketing Cloud, said using cloud vs. on-premises software is not an either/or proposition. "It's an augmentation and extension strategy where it makes sense," he said.
There's no "obvious use case for cloud that full-stop it's going to undermine on-premises, by any stretch of the imagination," said Ms. Munchbach.

However, once marketers make their way to the cloud, returning to on-premises isn't likely, said JetBlue's Ms. Miller. "That ship has probably sailed at this point."

Seth Fineberg contributed to this article.