When I’m researching a topic, I often have MANY tabs open before I’m through. It is often easier to again use (or slightly edit) search terms that have ALREADY been typed into the search box (from the search I just performed in the previous tab) when I open yet another new tab, rather than start again with a blank search bar. (It’s even more convenient than it would be to fill in the new tab’s blank search bar by having to choose my previous search term from a drop down menu.)
Dividing the one large search/address bar into two separate bars (one search bar, one address bar - as it is in Firefox, I believe by option?) allows you to open a new tab, while keeping the previous search term in the search bar of that new tab.
I notice some people prefer the leaner look achieved by the single bar, and although I do admire the uncluttered design of Brave (in more ways than one!), for me, the cumulative time-saver I mention above holds much more value!