Why 600MB of "BrowserMetrics"?

Also found in

.config/google-chrome/BrowserMetrics
/home/$USER/snap/brave/115/.config/BraveSoftware/Brave-Browser/BrowserMetrics

so it is something generic. Mozilla has a definition on what is does:

Goals & Objectives In order to understand how people use the browser and to evaluate our efforts to improve the browser, we need to collect and analyze usage data. There are many types of data that can be collected, such as:

• Session history navigation (to understand navigation patterns and improve the tab/window UI as well as backend features like bfcache) UI elements (which widgets are and aren't being used)
• Cache effectiveness (hit rate, bloat, etc)
• Memory usage (to understand how memory usage changes during normal navigation)
• Unsupported content (to understand how many people are affected and prioritize projects accordingly) "Problems" (unhandled exceptions in browser chrome, assertion failures)

Google has something similar.

Disable/enable:

• Open Chrome/Chromium, More, Settings.
• Under "You and Google" select "Sync and Google services".
• Turn on or off "Help improve Chrome's features and performance"

Mozilla/Firefox has it under "Sync" and "Firefox data collection and usage".

I am unsure if old cache files are removed if you disable it. You probably also need to empty cache (also found at settings).