I generally play two actions about 70% of the time if I'm not taking a game super seriously.
However, there are many situations where playing one action is much better, especially if you're the starting player in the next generation. For example:
1) You want to ensure your opponent skips first to protect your milestone or track bonus (probably in the next round).
2) You want to gain plants but are concerned about being attacked.
3) You have cards that depend on opponents' symbols.
4) You want to know whether the game will end this generation.
And I agree that selling a card may NOT count as an action. Controlling tempo by selling cards is allowed but can be a bit exhausting and tends to favor a greedier card style. Since TM doesn't have "active free actions," we could consider a house rule to test if this approach works well :p
However, there are many situations where playing one action is much better, especially if you're the starting player in the next generation. For example:
1) You want to ensure your opponent skips first to protect your milestone or track bonus (probably in the next round).
2) You want to gain plants but are concerned about being attacked.
3) You have cards that depend on opponents' symbols.
4) You want to know whether the game will end this generation.
And I agree that selling a card may NOT count as an action. Controlling tempo by selling cards is allowed but can be a bit exhausting and tends to favor a greedier card style. Since TM doesn't have "active free actions," we could consider a house rule to test if this approach works well :p