That's a great article and very enlightening, it shows how long it takes to finish a lipstick. This only reaffirms my belief that I don't need any backups whatsoever!!
That's a super handy link! If a lipstick averages 400 uses, and you apply once and reapply once and touch up once in the day, you'll be looking at a little under 200 days with that lipstick, or less if you reapply more often. So, you get half a year with your lippie if you use it daily or about 4 years if you use it once a week. I don't think this negates all BU's, because if there's something you love a lot, there's a good chance you're using it once a week through the year or multiple times a week during a certain season when it's the perfect color. If it's some really dramatic color you'd only use for special occasions or going out on the town, even if you love it, if you're only wearing it 5 or 10 times a year, it's going to take a decade to go through it, so yeah….BU's are sort of unnecessary there. Of course, the more lipsticks you own, the less you will ever need BU's too.
I know when I started buying makeup regularly, it wouldn't have occurred to me to back up. Then, because I didn't have many lipsticks, I saw I was really going through them, so there came this phase where I started to BU stuff I really liked. That phase had to end, though, because inevitably, I started having more lipsticks than I could really cycle through without taking extra steps. I'll still BU the most unusual and perfect colors - I BU'ed Punk Couture, for example, but there have been some great colors I loved that I assumed I wouldn't really be able to go through, like Reel Sexy, that turned out to get a massive amount of use. I BU'ed it later, through the Clearance Bin, but even that was a little hasty, because then All About Orange came out and there were multiple good replacements for RS, without having needed a BU. In 2013, I only BU'ed Punk Couture, Riri Boy, Runway Hit and Instigator, and I probably could have passed on Instigator. At least that one I'd be able to find a good home for. PC and RB are the top purples I own, other than Go For It, so those are getting a BU for posterity, even though I'm not going to manage using them once a week all year long (RB will get lots of use in the summer for daily wear) Runway Hit is just a perfect day or night color, so that one does get used a lot.
I think it might be a good rule of thumb that if you DO back up a lipstick, make yourself wear it at least once a week like clockwork or twice a week if it's a color you only wear in a particular season - then you can be confident you will get through it and get some use out of your BU.