Since the breakdown of Pokemon Go's 3-Step tracking system and eventual removal, websites like Pokevision have become immensely popular.

Websites like this are designed to help Pokemon Go users locate and hunt down Pokemon, by allowing the user to scan an area of the world map of either their current location or location of preference.

Besides from the geographical bias into finding certain Pokemon within the game (Water Pokemon more commonly spawning near water), Some Pokemon will be a lot harder to find in one area as apposed to another.   

Some people aren't physically able to wander around for hours on end. I understand the nature of the game is to go out and explore but unfortunately not everybody is able to do so.

Using Pokevision allows these players a fair chance to catch Pokemon they simply wouldn't be able to spend the time walking around looking for. It does still mean traveling to the location that Pokevision states, But limiting traveling time by a great amount.  

There is a time limit that Pokemon are in the game for, meaning that most players will be out exploring the world whilst using tools such as Pokevision anyway, in order to get to the locations stated within that time limit.

Besides all of that, Pokevision makes the game a lot more fun.