Promote to full health

[Robert]

If you leave a unit that can be promoted unpromoted, you can use it to recover to full health immediately when needed.

[weregamer1]

OTOH, you will be wasting that promotion, and you will still have to reach the full experience value for another level to get another promotion for the unit. "Saving" a promotion to waste this way is not a good idea - use the promotion to avoid taking the damage instead.

A valid reason to save a promotion would be if you don't know what you will be facing yet - for the early promotions, what terrain you will be fighting on. But also remember that the combination of huge penalty on defense in open terrain and nice bonus on rough terrain, means that most fights will be on rough terrain. (Also note that attacking a city does not count as either type of terrain for purpose of promotions that count.)

A valid reason for using a promotion on "full heal" would be that otherwise the unit is doomed anyway. You will have gimped the future growth of the unit, but that's better than losing it.

[pdxsean]

The more I've played the more I appreciate this advice. In theory, your units should be gathering lots of promotions over time. In practice, I rarely have a unit gather more than two or three promotions in a game. If a unit is built in a city with a barracks, holding on to that opening promotion can be pretty handy in the higher difficulty levels.

[weregamer1]

It must depend on your strategy and playstyle. If I'm doing much at all militarily, I always want the double XP policy by the time I start fighting CSes and other civs. I also husband my elite units carefully, allowing them to accumulate. In a game where I am not being a peacenik, I often have some units with over a dozen promotions. I once had a destroyer (upgraded from what was originally a frigate) that had actually run out of promotions to take - although in that case I had really won the game already but was waiting for my spaceship to finish, and was deliberately seeing if I could do it.

Also, the promotions in Civ5 are much more significant than in Civ4. Drill/shock add 20% to the unit's strength each, instead of 10% for the Combat line, and "air repair" lets your fighters and bombers never stop bombing.

[Jaybe]

Supposedly, with the (early?) December patch you will no longer be able to delay your promotions,
... or your social policies.