Add the ability to close a worksheet via the "File" menu.
In the fat client version of Excel, there's an option to close a file. Users accustomed to that would be less confused if that option was added to Excel Online.
At least a powershell command would be good for cases where a shared file gets uneditable.
Brett M commented
I think this idea is a good one to address the file locking issue - also described in this UserVoice item:
I keep hitting the issue where I use Excel Online to edit a file from SharePoint, close the browser window when I'm finished (as there isn't any other way to close the workbook), but if I or anyone else then tries to open the workbook in Excel (full desktop application), it says that it is locked for editing by me - even though I closed it! Eventually the system realises, but this is often up to 30 minutes later which is a pain if I am collaborating with someone else who needs to jump in to work on it immediately after I've made my changes.
@Dan - to address your question posted 20 July 2016, I think what the person has suggested as appropriate behaviour in the above linked article should also apply with Excel Online.
Frank Pike commented
Something has changed: now when I load (open) Excel, I can't close it--it stays on my screen regardless of what I try. I feel as though I am going in circles that keeps taking me back to Excel.
When I open an Excel file on a SharePoint folder I like working it online (feels cooler). However, I noticed there's no Exit command to return to the SharePoint folder. Sure, I can use the "Back" option of the browser, but I believe there should be an Exit button, I actually believe there was in previous versions.
What would you expect the experience to be if you chose that option in the Web Browser?
Excel word power point can use to edit online but after completing work File Close Option not found. which confuses where file is saved or not, File Close must be available,