You're going to think my answer is bizarre, but those kind of underpowered devices would be ideal for office work or non-IT businesses in general. They need computers to do the same things as they needed 15 or 20 years ago. Writing documents, spreadsheets, taking inventory, sending and receiving e-mail.
No, your idea is perfectly rational. Somebody I know consulted me on what kind of computers to buy for their new small business that would only be used for browsing, email, word processing. I found them a store that sold used Dell and HP workstations. They got 3 Dell machines (CPU + Monitor + Keyboard + Mouse), all Intel Core i5 with 16 GB RAM, 1 TB HDD with Windows 7 Pro, for $75 / each. We spent an additional $25 to purchase a cheap 128 GB SSD and installed Linux (LMDE), Firefox, LibreOffice and GNU Cash on it. (Preserved Windows Dual boot option, just in case they needed Windows for something). This was 2+ years ago and the owner was so happy that I reduced his IT hardware budget by a quarter. I recently purchased a used HP 25" monitor from Craigslist, for $60, in excellent condition and still having a year warranty on it, whose retail price was around $500 on launch. There is so much e-waste being produced ...
It's the same as with cars - companies want brand new because then you get a full warranty and theoretically you don't need to worry about it. So that $400 you saved would be spent in IT support for your old failing hardware.
But the thing is.....old PCs are really not that unreliable. If they survived the last 5-10 years then they are probably still chugging along just fine and for a small business there is literally nothing wrong with using them.
Well except the software.
OP said they got a bunch of computers, wiped them and installed Linux and LibreOffice on them - in which case the software is not a problem.
What about the software?
> Writing documents, spreadsheets, taking inventory, sending and receiving e-mail.
Well... Outlook is already a web app, the rest of the Office suite will follow rather sooner than later, and inventory - it's either web apps or SAP, both memory hogs.
But not all businesses need to use the latest versions of Microsoft Office. They might not even need to use Microsoft Office at all. iPads come with a stock e-mail application, as well as word processing and spreadsheets etc. And if you're using old PCs, you can use old versions of Office. Or WordPad and an e-mail client. They are light-weight.