Facebook's $16 billion purchase of messaging start-up WhatsApp isn't rational by any traditional financial metric, but the deal does launch a major salvo in the new war for time spent by users on their mobile devices, said Richard Greenfield, media and technology analyst at BTIG.
"This gives Facebook a tremendous share of time spent on mobile devices, not just in the U.S. but globally when you tack on Facebook plus Instagram plus WhatsApp," he said Thursday on CNBC's "Squawk Box."
The "crazy" price tag for WhatsApp has many people shaking their heads, like they did when Mark Zuckerberg bought photo-sharing service Instagram for $1 billion in a deal hatched over a weekend two years ago, Greenfield said.
(Op-ed: An outrageous price for WhatsApp? Hang on ...)
It's no wonder why Facebook would want to own WhatsApp from a sheer user perspective. With more than 450 million monthly active users—about 70 percent of whom are daily active users—the 55-employee company said it's adding more than a million new users per day. That puts it on pace to crack a billion next year.
"When you look at it on a valuation perspective, the price they're paying is only about $42 per [WhatsApp] user. To put that in perspective, Twitter goes for about $150, Facebook itself is about $140, LinkedIn $120,"said Robert Peck, SunTrust Robinson Humphrey Internet analyst. "It's not a bad deal."
But it's not about driving WhatsApp and Instagram users to Facebook, Greenfield said. "It's probably going to be about using WhatsApp to launch something new that Facebook creates."
Facebook is really good at being Facebook, but it's struggled to build other products, he continued. "Part of being a good CEO is knowing when you buy something and when you build it."
Peck agreed. "Not only do I think it's a great offensive move by Facebook, but I think it's a really great covering your flank, defensive move as well," he told CNBC.
Zuckerberg reached out to one of the founders two years ago, but really planted the seed with Jan Koum on Valentine's Day—just 10 days before the deal was announced. Koum, a Ukrainian immigrant, and American co-founder Brian Acton were former Yahoo executives.
Only time will tell if the WhatsApp acquisition was worth it, Greenfield said, because there's no traditional financial metric to measure this deal. "There's nothing that any investor is going to be able to rationalize this with on a basis like that."
(Read more: Facebook buys WhatsApp: A desperate move?)
Last year, WhatsApp made CNBC's "Disruptor 50" list—pointing out comments made by backer Sequoia Capital, which had said the mobile messaging service could become a more relevant social networking format than Facebook.
The venture capital firm's $60 million investment in WhatsApp has really paid off. That stake is now worth about $3 billion.
—By CNBC's Matthew J. Belvedere. Follow him on Twitter @Matt_SquawkCNBC. Reuters contributed to this article.