After the encounter1
As you said, the usual monster does as much damage as your healing surge value, so spending your action on Second Wind (SW) just postpones your defeat with one round, but does not actually help winning. The 10% increase in defenses rarely makes a tangible difference.
So in first approximation, you should not use it at all.
Second Wind is not a standard action for you
You are a Dwarf, or has other means to spend a minor or free action instead of a standard, like the Hunter's Resurgence feat2, or the Invigorating Stride power3.
Someone else spends the action
With the Swift Recovery power4, or something similar.
You still significantly contribute to winning
Rogues can use Sneak Attack only once per turn, so after you hit with Low Slash (minor action attack), you do not lose too much by not using your standard to attack.
Wildblood Wardens give sizeable penalties to marked enemies when they use SW.
With the Striking Resurgence feat Fighters can make an MBA while using SW.
However, each of these could do better:
- Low Slash could be used when you miss with your standard, so Sneak Attack is not lost for the turn
- The Wildblood Warden should be a Dwarf, and use the standard for something that actually helps winning
- The Fighter should use the feat for something better, and unless he is a Knight, standard actions should do more than MBAs
You cannot contribute anyway
You are unlikely to hit5, or completely unable to attack6. Unfortunately, these cannot be planned or relied upon.
If your best option is to spend a standard on SW, something went very wrong.
Only use it when you have nothing better to do, this usually means after all the enemies are dead.
- if you can afford to rest 10 minutes instead of 5, and you have an actual leader in the group, you are better off getting Inspiring Word or similar for the extra Xd6
- (Ranger, paragon) If you kill your quarry, you can spend your SW as a free action
- (Ranger, utility 2, move action) Shift your Wis, and spend SW
- (Heal utility 6, minor action) adjacent ally can spend SW
- blinded, or suffering from severe attack penalty
- immobilized, slowed, proned, or dazed and too far from targets