I’m not a tax or financial expert but personally from what I do know I think the main reason to open the 529 is because you would be able to take a state tax deduction (assuming your state offers it) on the money you put in and it for the year(s) you contribute.
It would then be able to grow tax free and you can use the funds you contributed as well as any growth to pay for your schooling and you would not have to pay state or federal taxes on the growth when you use the funds.
Be sure to check your state tax deductibility rules because some states allow you to take a tax deduction on your state taxes no matter which states plan you use while other states like New York where I live only allow you to take the deduction on your state taxes if you use that states 529 plan.
Also keep in mind with a 529 plan you can use it for yourself, your spouse, your kids and your grandkids and honestly any one else. You can change your beneficiary of the plan at any time and as long as the money is used for allowed educational expenses you good.
The important thing to keep in mind is that you are only allowed to use the investment options available to you in the plan. I have experience only with New York and Utah’s plans and both of those states only allow you to pick from very general allocation type plans such as a 70% Stock/30% Bond etc type plans and you can only change the plan a couple of times a year at most.
So at least in those plans investing in individual stocks or very specific etf’s are off the table and jumping in and out of the market is somewhat doable but not very practical since you are limited to only a couple of changes a year.
Hope that helps