Non-alcoholic beer is just soda flavored beer. It's a lot like chocolate soda flavored beer. It exists without reason or purpose simply for the sake of existing.
That said, non alcoholic beers do play a rather big social function here in Japan, where they have a ZERO alcohol policy for drinking and driving. The actual legal limit is BrAC 0.15 mg/L (equivalent to 0.03%). To put this into perspective, a piece of rum cake would set you over that limit.
A one time offense for drinking and driving in Japan (with zero altercations) is the suspension of your license for six month and a 5K $USD fine! The second offense is the permanent suspension of your license and up to a 10K $USD fine (my Japanese driver's education manual says this fine is actually up to the presiding judge). If you kill anyone in a DUI / DWI it's an automatic jail sentence plus anything else the judge wants to throw at you.
Japan has some of the strictest drinking laws I've ever seen.
That's where non-alcoholic beer comes into the equation.
In Japan, social drinking with work employees is ritualistic. There are several mandatory drinking parties a year -- even for public schools like mine!
New Years, is of course the biggest, but then there are PTA, Graduation, and start and end to the semester drinking parties. There's a Christmas drinking party as well. Every December 22nd all teachers receive a pledge form from their school that they must sign promising that they will not drink and drive and will use good judgement throughout the evening, even if they become intoxicated. The form is legally binding, so drinking and driving would result in losing their job!
Corporate companies have even more drinking parties, as they host foreign bosses and work exchange employees and every time there is a visitor or a tour of the factory / company, there will be a drinking party. In Japan, being a good host is vital to the identity of the Japanese people and part of their inbuilt tradition of manners and serving as a sign of respect. So, of course, such parties are mandatory.
With this amount of pressure to drink -- sometimes two or three times a week... non-alcoholic beer becomes the polite way to join these events without actually becoming an alcoholic, or getting slobbering drunk for that matter.
It allows employees to save face, pay the proper respect, be a part of the group, and not loose their driving privileges! It also allows women employees, who feel the same pressures to drink, to switch out to something that won't give them alcohol poisoning as they have to drink for two to three hours at the main party -- only to have to drink more at the ni-ji-kai or after-party.
The more you know!
(Classic Japanese beer ad snagged from Everything Japan)