In the “old days” of film, we had a limit of how much film we had with us, forcing us to think before shooting, as we only had so many chances to capture a shot.
Then came digital, but with small memory cards. Granted, we could shoot a lot more than with film, but there was always that chance of running out of memory. Memory cards are larger and much more less expensive than in the beginning, but we still keep that “max number of shoots” for this vacation in mind.
Now, with cell phone camera’s we’re also limited by our carriers bandwidth caps when it comes to how many photos to “transmit.”
All similar issues for NASA. Read this interesting description of how NASA decides what Curiosity can do each day.