Are you searching for boundaries and limits to the Next Generation Sync Client? You will found many information via Bing or Google, even if you search only on the Microsoft sites. And most of Microsoft sites do not have a date on the page, not every person may look into the HTML code and is able to read it. So it is not so easy to find the right page. and maintenance of published sites is complex, needs time… and it is easier, to write a new page, and again, without a date…

On the support sites of Office we find the right things:

SharePoint Online software boundaries and limits

So we see: SharePoint Online feature availability. Yes, that is right. Here you will find all limits to the current (and old) Office 365 plans for SharePoint. For example

File upload limit

10 GB – 1 byte (10,737,418,239 bytes) per file. In classic mode, upload methods other than drag and drop have a 2 GB limit.

Scroll down to the last section: Additional Resources 

OneDrive for Business restrictions and limits	To learn more about restrictions and limits when using the OneDrive for Business (Groove.exe) sync client, see Restrictions and limitations when you sync SharePoint libraries to your computer through OneDrive for Business. That’s the limits for the old Groove Client, Which you have to use right now for all SharePoint Server onPremises
	To learn more about restrictions and limits when using the OneDrive for Business Next Generation (OneDrive.exe) sync client, see Restrictions and limitations when you sync OneDrive for Business libraries through OneDrive for Business. Here you find all limits to the Next Generation Sync Client (NGSC)

Summary

You will see software boundaries for SharePoint Online, has nothing to do with syncing. If you use Groove.exe or OneDrive.exe as a sycn client you will have additional limits, you have to be aware.