There's actually something to what chip said. The average MLB salary seems to be increasing about 5% per year right now. Dansby will be controlled for his age 23-28 seasons as of right now, then we will have to extend him or he will become a FA. Let's assume for this sake that he basically becomes what is hoped/expected, since if not who cares about this. So he's a very good SS, sometimes an All-Star type. The Braves decide to extend him for another 3 years before the end of his deal, taking him to age 31. That's a pretty reasonable approach and would allow us to maybe move on as he begins to decline. Let's say we pay him something like this for those years:
2017 - $540,000
2018 - $550,000
2019 - $560,000
2020 - $3,000,000 (arbitration)
2021 - $6,000,000 (arbitration)
2022 - $9,000,000 (arbitration)
2023 - $22,000,000 (extension)
2024 - $22,500,000 (extension)
2025 - $23,000,000 (extension)
So we pay a total of $87,150,000 for his age 23-31 years and get 9 hopefully prime or close to prime years out of him.
Had we held him back last year and to start this year, then signed him to the same 3-year extension, you're taking him into his age 32 season, which is likely to start being a bit of a drop-off. And you will pay more for it. Taking the 5% increase into account, you're looking at something like:
2017 - $540,000
2018 - $550,000
2019 - $560,000
2020 - $570,000
2021 - $3,150,000 (arbitration)
2022 - $6,300,000 (arbitration)
2023 - $9,450,000 (arbitration)
2024 - $23,100,000 (extension)
2025 - $23,625,000 (extension)
2026 - $24,150,000 (extension)
So you're paying a total of $91,995 for most of his age 23, then his age 24-32 seasons, so 10 total. So obviously you can argue that getting the age 32 season at a discount is worth it. But you're not getting it for free, you are paying an extra $4,500,000 or so for it. Almost certainly worth it unless he drops off, but it is a slight extra cost to consider.