We would actually suggest changing the ownership of the files and folders which you've uploaded using SFTP to your normal user username using chown,
chown user.user folder -R
Basically logging using a normal user account and then switching to use is a security practice in itself or using sudo for performing administrative tasks.
Changing the primary group of a normal user to root(0) means your normal account password/account gets compromised, the attacker can write/delete files/folders where the group ownership is root. This is not a recommended way and opens a possibility for a compromise.