The problem is that small changes are barely worth reviewing. Also a series of small changes can obfuscate the larger context of all those changes.
Each small change on its own might make sense and be ok to a reviewer, but if you step back and look at the series of changes together there might be some issues that could have been noticed.
There is an easy way to resolve this:
Git makes this exceptionally easy -- it's certainly far easier than reviewing a large document with Word track changes!