Maybe your character is squishy, and can't afford to take risks? Should a player be punished for playing carefully? Maybe you are playing a character that is careful by his/her very nature? Should role playing be punished?
Yes, they should; however, if being careful is part of the character’s personality, and they play it that way, then they should receive xp for roleplaying well. I also consider the characters contributions to the story.
For example, in one of my current campaigns, one of the players has an Elan Psion. His character believes he is a God and he does not like to get his hands dirty. Everyone else does the fighting and he stands back watching and gives orders mostly about who to kill and who to save. When it’s all over he applauds their party’s actions, then he scoops up those that were subdued and begins preaching to them about the wrongs and he works to “convert” those the party has beaten. His character adds a lot to the story that helps him keep up with the party in experience while limiting his involvement in much of what the party does.
These are the reasons why I don't presume to know why my players do what they do. I just let them do it, and do not punish them for it (unless they do something really stupid).
Not giving a player experience or giving them less experience than the rest of the party isn’t a punishment. When I give experience I AM rewarding the players for their involvement in the story. The amount of that reward should reflect their contribution.
I don't want to always encourage my players to take risks, because sometimes caution is called for.
And in those cases, I would argue that being cautious should be rewarded, especially if the party develops a creative way to handle the situation.
By rewarding them based on their contribution.
If I get my players into this mindset that they must take risks, or they'll miss out on exp, then that could very well ruin the game.
That is a possibility, or it could make the game more fun as they push the limits of their characters and start coming up with creative solutions to your challenges. You really won’t know what effect it will have till you try it.
I want my players to role play their characters in the way they feel comfortable playing, and in the way they think suits their character.
The reward them for good roleplaying, especially if that suits their character.
Some players play careless by their very nature. I have such a player in my group. He takes rash actions, and risks, and often gets into trouble. Sometimes this works out alright, and sometimes it doesn't.
And the reward he receives should be commensurate with the contribution to the story and the benefits, or peril he brings to the party.
But another player in my group is a less experienced role player. He prefers to not take risks, and often needs the DM to give him a moment in the spotlight, so that he is not overshadowed by the rest of the group. Should he reap less rewards? Should I punish him for the simple fact that he's not as experienced at D&D as the rest? Do I want him to feel left behind? Do I want him to feel like the lesser player of the group? ...All of these are negative reinforcements.
Not at all, but again, the reward he receives should reflect the character’s contribution. I have a player that is new as well, and he needs plenty of encouragement. I frequently stop play, and will describe the situation just to him. I ask questions about how the situation makes him feel, and how he would respond. Then I turn the question around and ask if that is how his character would react. Usually the answer is no. “How would he react?”
I encourage him to push himself to roleplay the character, then I reward him accordingly. The only way he will get better is by testing what he can do and attempt to push the limits of his imagination.
My take on this, is that I reward the great moments of any of the players with experience for the whole group. I find that it doesn't encourage players to lean on the more pro-active players. Instead, it encourages them to role play too. It makes it fun for the whole group. No one gets left behind. Everyone adds to the reward for the whole group, and this helps to get them to keep working together.
To each his own, as I see it, rewarding group experience doesn’t encourage team work, it discourages individual creativity, and limits the character’s roleplaying contribution to the storyline.
Also, experience variance isn’t a punishment. It’s a differentiation of contribution. You want more xp contribute more, if you don’t care contribute less. Besides, the reality is over time it all balances out, because one day John may be very active, but the next he won’t be. He’ll get lots of xp one day, and the next he’ll get less.