Second space is just like 2 users in one phone. You can create a new space just like a new phone.
It is easy to switch between both the users but needs the password. So if you want to hide some important documents or social accounts, email use second space option.
Usually, people ask our phone for calls or messages. Some people like to see your phone specification but started watching your personal stuff. In this case, you can turn on second space and give it to them.