On mixed use trails I tend to call out "on your left" to walkers/runners as I'm rolling down on them - unless I'm out of breath and going really slow, then they tend to hear me and look back . But if they have ear-buds in I don't call out anything half the time.
For other riders, it depends on traffic. If I have plenty of room to pass, I may go by without saying anything. And if there's on coming traffic, well actually the levee path is narrow enough that I'm not into a game of chicken, so I hold back. Seems like a lot of the time I'm the passee not the passer when it comes to other cyclists on the levee path.

Kids - I yell to them no matter what because they're always all over the place. There were times I've had to call out "up the middle!"

On roads, I may be passing closer by, and then I do tend to call out. Again it depends on the road and the vehicular traffic load.