Why add an email to work?
If you're not sure if you should add an email to a piece of work, ask yourself these questions:
Does the email contain attachments?
Are there several steps you need to take with this email?
Is or will this email conversation eventually end up into a larger project/job/work?
Does the email pertain to an existing work item?
If the answer is yes to one or some of the above, add that email to work or create a new piece of work directly from the email. Any attached files will be stored on the Details tab of the work item, and you can keep track of everything that needs completing by using Tasks.
Best Practice Tips:
You can copy text from the email and paste it directly into a Task list.
If the email pertains to work AND requires you to take action, you can do both. Add the email to work AND add it to your to-do list.
Why create a To-do item for your email?
At any time you can create a To-do for an email. This is handy if you want to reply to the email later or have one of your colleagues' reply to it for you. You can do this by assigning the email to yourself, putting the email on your to-do list, or by assigning it your colleague, putting the email on their to-do list.
Further reading: Effectively Managing Triage