That only exists in San Francisco. Anywhere else, we are pretty much blind without cheating tools. Besides, the Sightings system is only helpful in areas with high pokestop density: Without it, the system wouldn't help: There are ZERO pokestops in a one mile radius around me. The nearest area with pokestops has 5 clustered together in a park... that has no pokemon spawns barring luring pokestops.

Third party tracking systems let me go with my son pokehunting in my subdivision: we could see a pokemon we want, and leave the house to look for it. Without that, the game is no fun, as a typical trip will only yield pidgeys and weedles.