When a file is renamed, and also contains changes, it isn't easy to view the changes from "Check for modifications". It would be fantastic if you could diff the new and old file directly from within "Check for modifications".
Of course this issue arises because SVN treats the rename as a delete and add operation, so the deleted file no longer exists to compare with. The typical scenario is that you are reviewing someone else's code changes, and they have renamed a file, perhaps even moved it to a different folder, and have also made code changes within that file.
My current workaround is to revert the deleted file(s), then go into the folder in question, select the original file and the new file, then diff them there. It would be a really nice workflow if you could do this directly in "Check for modifications". e.g. if you could double-click on a renamed file just as you would with a modified file, and it was intelligent enough to figure out that it was renamed and show you the diff.