From reading the doc, it is of significant note that it's expensive to maintain that index, as it needs to be re-computed for every insert and update. It's not something to take lightly. However, it might make sense to do this on a relatively static database, or one in which the maintainence time is irrelevant, but access time is key.
Feel the white light, the light within
Be your own disciple, fan the sparks of will
For all of us waiting, your kingdom will come