Is there any redeeming value to playing this game or is it just entertainment?
I do learn some new words from time to time, often by experimentation when trying to maximize high value letters and squares. There’s also the option to turn on messaging that’ll send notifications, one of which is the “Word of the day” and that can be something new and interesting.
Also, if you’re serious about it it does provide reasonable brain stimulation, never a bad thing. If your opponent is a close match a bit of strategy is required, often times it’s unwise to play the maximum value word you might have because of what that might set them up for.
Beyond that, yeah, it’s entertaining too. I usually have 15 to 25 games going on with several different people at any given time so there’s always something to do when eating lunch, at the airport, during commercial breaks, etc.
It makes you good at Scrabble when you find yourself playing a game with your Mom on Christmas day! 
For me it’s mostly entertainment. I never find myself suddenly using words like QI, ZA, or QAT in my daily speaking and writing.
And, in much the same way that I lose to non-musicians all the time at Guitar Hero in spite of being a very good guitar player, I beat people all the time at WWF whom I know to be far more literate than me.
I know they changed their name to WWE some time ago, but this still provided a momentary wonderful image for me, so thanks 
Right, QI and ZA don’t come out of my mouth unless I’ve actually put QAT in it.
Two women who work for me play during the work day. One of them showed me how the other scores waaaay higher in the evenings. They have agreed not to cheat, but obviously the one woman is cheating like crazy when at home.
So one redeeming value is getting to know how your friends roll.
ZA, I understand, but who decided that ZAS is a word?
I always considered “za” to refer only to the collective of pizza - to paraphrase Homer Simpson, “it’s ‘pizza’, not ‘a pizza’.” (The original replaced “pizza” with “lamb”, when trying to explain to Lisa the difference between a lamb they met at a petting zoo and the lamb chops for dinner that night.) “Let’s get some za” would be a correct usage, but “let’s get a za” would not. As a result, “za” would not have a plural.
This is so crazy to me. To cheat at that game would drain literally all the fun out of it for me. To me, the main attraction of Words With Friends is that it can be played in the 20 seconds I’m in the elevator (for instance), or I can make dozens of moves over lunch, with my sandwich in my other hand. It’s a fast, casual, ultra low-stakes game for me.
To have to bounce back and forth to a Scrabble cheater app or website would instantly make the game so tedious as to not be worth playing. I’d much rather lose (and I have several opponents, my wife one of them, who beat me at an 80% clip) than cheat. Ick.