1. Heavies can do a ton of damage behind your lines. Best to let them get "stunned" for a turn than slightly damage enemy.
2. You can and will take double shots in one turn. Useful.
3. Sniper + MEC's kill 80%+ and you don't want your will to lower.
4. Once again, VERY expensive... you got MELD to burn this could go either way
5. Other skill worthless and jumping for high ground OP. Need I say more?