Finding things in Finder · Storage Studio in Finder's sidebar
Do I still need the Google Drive, Dropbox or OneDrive app if I use the Storage Studio location?
Short answer: Not to browse those accounts in Finder — the Storage Studio location shows every account connected in the app. Keep the providers' apps if you use their extras; the two are separate, and you can hide duplicates in the Mounting tab.
Not to browse those accounts in Finder — the Storage Studio location shows every account you've connected in Storage Studio, with files downloaded when you open them.
You can keep the providers' own apps if you rely on their extras, such as offline folder syncing or their sharing tools. The two are separate, and each shows its own folder in Finder's sidebar.
If both show the same account, you can hide one in Cloud Accounts → Mounting to keep the sidebar tidy.