I’ve never really payed attention 
Honestly I’ve probably only retreated like 3 times in a year. I always try and pray for a lucky cascade to turn the tides.
Retreating will always cause 1/3 of max health in damage to each characters. This can potentially knock one out and cause an extra wait for respawning.
You should do that more often. If your team-health is full, and you are going to be hit by Sniper rifle that kills one of your toons, retreating is best solution.
You will lose 1/3 health, but you can try that pesky node again.
Retreating really is viable tactics sometimes.
Minor correction, it’s 33%. Meaning if you retreat three times in a row quickly, you’ll still have 1% health remaining. That .3% makes a difference! 
BZZZ Wrong answer. It’s 1/3. The 10 health you have remaining after 3 retreats (which is constant across most characters, no variance for total HP) is the amount you regen between fights if you retreat 3 times in a row. I just ran a test, Juggernaut with 400 health and MBW with 175 health. With 1% remaining Juggs should have 4 and whatever he healed, and MBW should have 2 and whatever she healed, but they both have 10 HP.