Flavor packs are popular in kit wines, and I think that is where the term came from, the kit makers. Kits like them because they make the flavor issue a no-brainer for all experience levels.
But IMHO, a good goal for the from-scratch winemaker is to get to where you don't need them. That's probably why most scratch recipes say nothing about them. I think of the f-pack as an attempt to correct a pretty serious deficiency in the original wine recipe or the process used. This is where a well-kept wine log is your best friend. On subsequent attempts, you can adjust the recipe to meet your goals by referrring to exactly how you did it before and changing quantities/practices in an effort to get closer to your goals. You get to drink your "mistakes" while you seek out a more perfect recipe. What's not to like?
My twin goals are to ideally use no back-sweetening and to use no f-pack in my wines. There's nothing "wrong" with either one, but by having these goals it gives me something by which to judge the outlier wines that didn't meet them and how far they fell from the goals. Then I adjust the recipe next time, and try again. For example, if I want a semi-sweet wine and also have the goal of no back-sweetening, then I am going to have to back up, look things over, and change my process from the typical recipe that ferments totally dry and then is sweetened.
My goals come from a personal impression that the taste of wine that has come with no adjustments through the fermentation process is cleaner and more complex. Plus, having the goals keeps the fun in it, and encourages me not to just hop from one recipe to another but to work on perfecting them to hit my targets. The only exception is my wine-juice blending experiments, in which I am still learning much.
Right now, I have a blueberry wine in the first racking that I stole from yesterday to taste, and -- if I don't screw it up -- it is on-track to meet both my goals. I hope I've not jinxed it now by mentioning that!
Fingers crossed.