The Spawning Pool is the first Zerg tech building; it unlocks Zerg's basic fighting units - Zerglings. Building the Spawning pool also unlocks the Lair, Roach Warren, Baneling Nest, Spine Crawler, Spore Crawler and the Queen.
The Spawning Pool is a high priority target for the opponent, so it is advised to place it somewhere hard to reach. For most of the first year of the game, conventional wisdom dictated that the safest spot of a base was behind the mineral line. However, the increasing prevalence of drop play has suggested that the middle of the Zerg base may be safer. However, placing the Pool strategically near the mineral line can prevent enemy scouts and harassment from easily maneuvering around your workers.