)
The original Torah commandment is to refrain from doing melakha on Shabbat. The Sages added a protective fence by prohibiting even deriving benefit from melakha done on Shabbat. Therefore, if a Jew turned on a heater in a cold room on Shabbat, another Jew may not benefit from the heat. Rather, one should leave the room or open a window to avoid deriving any benefit. If a Jew turned on a light on Shabbat, another Jew may not benefit from the light. However, one is allowed to do anything he could have managed had the light not been turned on.
A Jew who did a melakha on Shabbat unintentionally, is permitted to benefit from it after Shabbat, as is everyone else. In contrast, if it was done intentionally, none of the people for whom it was done may ever benefit from it. For example, if a restaurant owner cooked intentionally on Shabbat, the food made may not ever be eaten by the owner or any of the owner's customers. However, other people may eat it after Shabbat.
