Sealing a bunch of food in a pressure cooker such means you can't really stir the contents, which can lead to a bit of scorching from time to time. This isn't a huge deal, but it can lead to some unsightly burned-on gunk. Luckily, it's pretty easy to get off, you just need to enlist a good friend.
When you can't get burnt food off your insert with soap and elbow grease, this stuff works as if by magic to restore your insert to its former, gleaming glory. (This also works with other pots and pans.) Just rinse the pot with a little water to get it damp - you don't want a lot of water pooling. Scrub in a circular motion with a soft sponge or cloth for about a minute, then rinse (thoroughly) and dry.
Return the insert to its home, and continue cooking all sorts of tasty things in your favourite pressure cooker. If you are unsure of where to purchase this miracle cleaner, here is the bar keepers friend's website with a list of all the places you can purchase the cleanser in Australia.