I don't know what you consider ideal conditions, but we do it all the time. It's pretty common for me to be reviewing a document and see the avatars of other people who are simultaneously reviewing and editing it. I've been doing this for years and have yet to have a problem.

Sharing multiple copies of the "same" file is where the problems come in.

There are multiple issues. [1] If you drag/drop or upload the file to Teams, it creates a copy and shares it via Teams SharePoint?

[2] If you look in Teams, some people have automatic permissions because they are in the Team or already have access to the Teams folder. If they are not in the Team, then you have to give "direct access".

[3] For the paranoid, you first go into OneDrive and "manage access". Then you are faced with two choices whose UX is confusing to say the least. One option is to "Copy Link" which has almost the same identical choices as "Share with Specific People". Note that "Share with Specific People" gives you options like "Anyone/doesn't require sign in" and the dialog has a button called "Copy Link". Huh? I thought I was sharing with specific people. I am still unsure who exactly can see the document. Or if the document was shared externally outside of my company.

SHAREPOINT https://support.microsoft.com/en-us/office/share-sharepoint-...

ONEDRIVE https://support.microsoft.com/en-us/office/share-onedrive-fi...

Below are snippets of MSFT's documentation of what happens when you upload a file to a Teams channel. I BOLDED the confusing parts and added ???.

> All files that you upload, create, or share in Teams can be found in the ONEDRIVE??? icon app on the left side of Teams for desktop.

> Files that you upload to a channel are stored in your team's SHAREPOINT???folder. These files are available in the Files tab at the top of each channel.

https://support.microsoft.com/en-us/office/file-storage-in-m...

With Teams, the distinction is pretty easy: Within a Team, the file gets uploaded to the Team's SharePoint site. If you share a file in the Chat module, it gets uploaded to your own OneDrive.

It's clear as in "if you know the rule you can count on it" but there is no discoverability within the tool itself. It will even say if a file has been uploaded into the chat already, giving you an impression that the file is in the chat - while it really is in your own onedrive.

I only discovered it by chance while roaming my onedrive directory.

On top of that, Onedrive is the worst of the lot at handling collisions in files. I routinely find that files I work on using two machines in my office (gbit uplink) get garbled. To the point where neither has the latest changes, they’re just gone. Absolutely terrible.

Confusing to the points where I had (university) students that told me "I _only_ have the file in Excel [and therefore can not share it with you]". That statement confused me until I left academia and was forced to work with MS Office for the first time. Having files in 4 different locations really does not help.