It has limits, but it is usefull when you know the limits and how it is ment to be use.
First of all, the limit is 1TB and will later be without limits. My thoughts on that, is that we dont use that much Storage, so it doesn’t consume that much physical Storage anyway.
There are two different limits, it is the synchronized limits and the uploading limits.
When we synchronize to OneDrive for Business with the OneDrive for Business Application, or the combined OneDrive and OneDrive for Business Mobile App, there is a limit for 20,000 items and file size of 2gb.
Files and folder names also has limits to 256 characthers and 250 for folders. These are also general limits for SharePoint Online wether synchronized or not.
Certain characters are not allowed either:
/ : * ? ” < > | # %
aswell as files starting with (~) isn’t supported.
Source: Microsoft Support Article.
Type of files or fileformat not allowed in OneDrive for Business are surnames like tmp, ini, db, etc.
Source: Office Support Article.
Remember that open files are not synchronized, so untill you Close the Application the file will not be synchronized to OneDrive for Business.
When that is said, we are working across the Internett, so to many files or to large files will seem unsupported. Where it begins to hurt depends on your Internet Connection.