Try to place near the ground, as the player will drop from the entity origin to the floor. Also, make sure the info_player_start is clear of any obstacles, or the player may be stuck at the start.
In Counter-Strike, this entity is used for Counter-Terrorist spawn.
For multiplayer games/maps, if none of the appropriate starting point are found (usually info_player_deathmatch), then info_player_start are used as "backup" solution for respawning players. So it's a good practice to place one even if you are making a multiplayer map.
In DeathMatch Classic and Half-Life, this entity can act as the (re)spawning location in "free look spectating" mode unless the map has a trigger_camera entity.