Vermiculite is best used in applications where a pot or growing bed needs to be filled with a growing medium. For example in hydroponics vermiculite can be used in a wicking bed system where water from the water basin below is sucked into the upper reservoir by a wick or the vermiculite itself.
It can also be mixed in with other growing mediums such as perlite to get a cross between the main features of the mediums (perlite has great aeration/oxygenation properties, and vermiculite has great water absorption and retention properties) - mixing them together means you can suit your growing medium based on the characteristics of the plant that you are growing.
Love my smart soil! I have rewashed it and reused it a few times and still things grow great. I would probably only get 4 uses out of it though, as the vermiculite starts to get smaller and smaller after multilple uses.