Keyboard shortcuts let you keep your place in an email list
Switching keyboard shortcuts on (Mail Settings - General) has the added bonus of highlighting the last email you viewed in a list with a little blue bar on the far left.
If you are used to Outlook, you may get frustrated that Gmail doesn't highlight which email you last viewed when switching back to a list. However, if you switch keyboard shortcuts on (Mail Settings - General Tab) the email you last clicked on will be highlighted with a blue bar to the left of the email. You need to get into the habit of using the back to inbox button rather than the Back Button in your browser for this to work. We're not sure why you need to have keyboard shortcuts turned on for the bar to show but it's a very useful tip!