This page allows you to rebuild the index used by the Tag Plugin. This isn't needed generally as the index builds and updates itself while you tag your sites. However if you just upgraded, added or removed a lot of files it may be a good idea to cleanup the the index.
This Manager needs a recent browser as it makes use of modern JavaScript to carry out multiple tasks in the background (using AJAX).
Rebuilding the index takes a long time. You should leave the page open until the indexing has finished.
Making a backup of data/index/tag.idx is recommended in case something goes wrong during rebuiling.