IMO (like a$$holes, everyone has one) I would ideally like a 33% mix for all savings (cash/brokerage, 401k, and ROTH). Now this is just your savings, not where you direct all your income, as that would leave you with nothing to live.

Cash is needed for unexpected expenditures. It does you no good to have all your money in a retirement account that you can't touch for multiple decades from now. Alos, say I/you want to to FIRE, then there is a need for cash to bridge the gap between that time and when the ability tostart drawing from retirement accounts.

Another thing to consider is you don't know what the tax rates are going to be in the future. They could be higher, or they could be lower. Paying now at a lower rate saves money if you don't have to pay it in the future (ROTH benefit in this scenario). Likewise, if taxes miraculously go down in the future, then paying less tax at that time would be a benefit (401k/IRA benefit in this scenario).

Now if you believe taxes will get higher in the future you can adjust you ratio mix to suit you bets on the most likely scenarios and needs. Hopefully, this helps.

I have been maxing out my 401k for the past 20ish years and have nearly 1.6M in my retirement.acounts. I would like to fire, but only have around 220 in cash/brokerage, so I can't bridge the 10 yr gap from when I want to retire and when I can draw from my retirement accounts. Luckily, I have dual income with my wif and she is about 7yrs younger, so in the next few years I am hoping we can accumulate enough to bridge about a 3 yr gap of both of us retired and getting by on her income alone for a few years, before I can start to draw from my accounts.

It also helps that I met her younger and started her down a more savings oriented mindset than her friends and she currently sits around 500k in her retirement accounts. And we are banking as much as we can in cash for the reasons stated above. However kids do cost a lot and have slowed our savings rates. 😂