3 Answers
Nikka is spot on.
The only tasks you should do with the root account is restricted account tasks.
For everything you should have one or more Admin/User/Service accounts with the least rights needed for the suite of tasks.
🙂
Yes, you should check the last usage. You can also use CloudTrail to identify where that key is being used.
Also, you can just deactivate the key, as a first step. Leave it for a short period and see if anything breaks. I’ve had similar before, e.g. a DBA had configured his user key to do automated tasks. When he left and his account was deleted (not by me), things broke.
I personally prefer to disable for a period, then delete when no one screams.
I guess that you should’t use your root access key for the other services, but create other users instead.