It's a real rush when they do up the final arm straps and you feel your arms flatten against your chest. You try to move your hands and you know that you aren't getting out. You try to struggle free, but you can't move it. If the back is done up right, you don't even need the crotch strap. However, if you're going to be left alone, it's safer to keep that in place.
I had one and used to do some self-bondage, but strapped myself in too tight one day, After about an hour of struggling, I finally had to pry out some scissors and cut the sleeve to get my hand out. I ended up cutting my hand as well, but I was able to get free.
It was a real rush, but I ruined the jacket as well! I haven't gotten a new one since.