1. Pro : Get him at a discount
If you're Lauri Markkanen, you may make more money on the open market. In 2025, Markkanen could be one of, if not the most vaunted free agent to be had. It all depends on how the next season shakes out. Still, security is important, and getting him locked up to a new deal now means just that. The cap could go up between now and then, which means Markkanen could make more money, but it could go down too, which means could make less money. Regardless, it seems like the smart move for both Markkanen and the Jazz is to strike now.
Unless he's asking for a LeBron James-sized deal, Markkanen will be far more affordable than any potential free agent option in 2025, and he'll likely agree to less money than what he could ultimately make had he gone into free agency.
1. Con: May overpay
There's always the possibility that you re-sign him and he falls out. Careers go up and down and performance fluctuates. Markkanen could go from an All-Star caliber player to a guy barely deserving of a starting spot by the time the contract is over. If he's not producing, then it's very likely the contract will far exceed Markkanen's worth, and that's the risk you accept when you start the early negotiations.