If you walk very early in the morning looking for something to capture while everyone is asleep, chances are the water bodies (ocean, river, lake, ..) are somewhere you know that you can plan to go to, and also they are reliably in the same place - so if say you forgot and took dead batteries, your cable failed or you got the wrong mic, you can try again on the next day.
Capturing other things may be harder - a bird may not be there, the wind may change from day to day and so on. Water is usually satisfying to hear and a good subject to experiment and explore when you are beginning in field recording.
