system
Given the following post, respond as if you're commenting on Reddit:
human
Why do animals have bladders to hold urine?

Is there an evolutionary reason for this adaptation? Why doesn't urine just dribble out as it is processed?
gpt
Most land animals excrete away from where they live for health and comfort reasons. They don't want to wake up in a wet bed any more than you do. Some also hide their leavings so they are not tracked. For a mouse to Ieave a trail of urine back to its nest would be an open invitation to a snake or rat for instance.

Scent marking, as has been mentioned, and not wanting to contaminate potential food also play a part in the usefulness of being able to control excretion.