Insight on both a Roth IRA and Trad IRA?

I have a 401k at work that I have been putting 20% of my check in for at least the last 15 years, 5% in work Roth 401k and then a separate brokerage account with Fidelity for rainy day money.

I was thinking about changing some of those %s to funnel into a separate Fidelity Roth but want to see if there were any benefits to also having a traditional IRA. I would probably hit both contribution limits for both IRAs. My plan is to zero work Roth 401k then 6% 401k > max separate Fidelity Roth IRA > max traditional IRA > rest to brokerage account

I know a lot of it has to do with tax brackets at retirement but any insight would be great if people go with both IRAs (Roth and Trad) and a brokerage account. I’m late 30s if it matters

Edit: I guess my question is why people would go with both IRA types? I saw on the Fidelity FAQ that some do both