I have hunted elk in WY (my home state - though now live in MN) with a rifle, bow, and crossbow. I have seen the good, the bad, and the ugly with crossbows. First to answer your question, the safest and easiest way to discharge the crossbow is to simply carry a bolt with a practice tip in your quiver so that you can shoot it into the dirt. I do not cock the crossbow until I am at my spot or know I am getting close to game (not too close so they can hear it though as cocking can sometimes be a bit loud). I will still hunt with a cocked and loaded crossbow but you need to be really careful knowing where you are pointing that thing at all times.
The Good - 2003 - Shot a nice 5pt elk with crossbow. Double-lung pass-through, great blood trail, quick, clean kill.
The Bad - 2003 - Same year, my friend also shot a nice 6pt elk with my crossbow at less than 10 yds. No pass-through (must have hit bone on opposite side. We left bull alone for over an hour before tracking and found bull (alive) less than 100 yards above us. Bull was sitting up but could not get up. Needed to put a couple more in him to finish him off.
The Ugly - Can't remember year 2007ish? - I shot a smaller satellite bull with a crossbow. Shot placement was good, but for some reason I did not get great penetration. Good blood to start with, but ended up losing blood and could never find bull. Tore up my tag, done for season. My friend had bought new bolts for the crossbow that year. I think the "bolts" were really cut-down aluminum arrows. I think they were simply too light to get great penetration.
More Ugly - 2011 - I called a huge 6pt bull within 20 yards of my cousin. He shot and got complete pass through. Waited several hours believe we had a dead elk on our hands. Good blood to start. Blood trail disappeared. Ended up losing this bull. Heartbreaking. I think he may have shot low into brisket.
Lessons learned...
1. Make sure you have a good set-up and good carbon bolts and broadhead or some other set up so that you get good penetration.
2. Do not get crazy on distance. Lots of people think just because its a crossbow you can shoot out to 70 yds no problem. Again, its all about your set-up.
3. Practice...just because its a crossbow doesn't mean you should not take it seriously or practice as much as you would with a compound.
4. And like with any weapon...its all about shot placement.
The jury is still out on crossbows for me though I do enjoy shooting them. I using my compound in WY this year. My cousin will use a crossbow. I am hoping to see only the "Good" this year.