In the games
In Pokémon Red, Blue, and Yellow, lookout stations serve to separate two areas, and also to guard the corresponding route, which is why an Officer usually resides inside. Upon speaking to the Officer, they may offer words of advice or information about the route or city that the lookout station guards. In Generation I, certain lookout stations contained a second floor that contained a spot where binoculars could be used to see faraway landmarks, or even certain Pokémon. This generation also contained certain lookout stations that prohibited entry until the Officer, who claimed to be thirsty, was given a drink that could be bought at the Celadon Department Store. These lookout stations all lead to Saffron City.
Much like Generation I, lookout stations serve to separate two areas. Unlike other buildings, the player can often ride their bicycle through these buildings to guarantee fast transportation. Randy, a non-player character, will give a Spearow to the player in the lookout station north of Goldenrod City.
Lookout stations were sparse in the Generation III games set in Hoenn. There are just two lookout stations, each connected to the Seaside Cycling Road. Players may not ride bicycles as they travel away from the Cycling Road, but are forced upon their bicycle if traveling toward it. If the bicycle has not been obtained, they may not enter.
In Pokémon FireRed and LeafGreen, lookout stations serve the same purpose as in Generation I. Because players can now trade items attached to a Pokémon, the key item Tea was introduced. This served the same purpose as the drink from the original games. Professor Oak's aides will meet the player on the second floor of some lookout stations. He will check the Pokédex, and will reward the player if he or she has caught a given number. Lookout stations exist also in the Sevii Islands, giving access from the port to each town.
Much like in past generations, the lookout stations in Generation IV serve to separate two areas. In Pokémon Diamond and Pearl, the player cannot ride their bicycle through these buildings, but this is possible in Pokémon Platinum. Officers do not watch over the route, but other travelers can be found inside, as well as a map showing the player's current location.
The lookout stations, however, also have a practical use within the games' programming. As a player moves from route to city, the map tilesets (textures in Generation IV) must be loaded for each. While this is easy when a city connects to relatively few routes, where all can use the same tileset, areas like Saffron City and Jubilife City, which connect to many different areas, would need to load multiple tilesets/textures, potentially slowing down the game or even crashing it. The programmers, realizing this, broke up the overworld with these gatehouses to assure crash-free gameplay, and to properly display the routes/towns/cities.
List of lookout stations