You get locked into more trips, and hooked on the good times. I got a 'great deal' on annual passes I probably would not have otherwise bought, and am now taking am extra trip this summer because it is "free". In reality, I paid for those passes and will be buying meals and many, many dole whips.
We went in May 2015, Feb 2016 and April 2016 all on 1 AP. And we weren't
DVC owners yet! (But I see now this is how it happens...)
May 2015: I had a work conference in Orlando (not at WDW), and we would have had to pay $$$$ for child care while I was gone. So, if we paid "a little more" DH and DD1 could go to WDW instead, and I joined them for a few days after my conference. Not coincidentally, this was our first stay in DVC (BWV), on a cash reservation (happened to find a great deal), on which we got upgraded from a studio to a 1Br. I was about 7 weeks pregnant, too. We bought APs and TiW because we already knew about trip #2...
Feb 2016: DH had a work conference in Orlando (not at WDW), I was on maternity leave, I did not want to be home alone with 2 kids (and paying $$$ for childcare) while DH was in FL, so, for "a little more" (2 airfares) we went to WDW. Also, turned it into a family reunion trip with my sister, her partner, their 7 mo old, our 3 month old, our 4 yo, and my parents. We rented points for a BLT 2br. "Saved" a ton of money on park tickets and meals thanks to TiW...
April 2016: I was near the end of my maternity leave and wanted to go on a fun trip before going back to work. Found a good deal on GF. Priced out other options (for beach vacation; baby did not have a passport yet so we had to stay in US). Park tickets are "paid for" and we get a 20% discount on meals, Disney is easy with a baby .... we're off to Disney again!
We did not go again until August 2017, 16 months later, and it felt like a really long time after the 3 trips in a year. This trip was on points rented before we had bought DVC, by by the time we took the trip, we already had our BLT contract. So... once we banked 2017 into 2018, we had points we "had" to use in 2018, and DD2 is turning 3 in 2018, so ... now we have 2 trips booked in 2018.
That's how it happens...