well u only will be able to use them if u are planning to use them b4 the game start...else it's hard to consider them cause usually after u get hive...u can js go ultra or mass hydra or cracklings which is cheaper n faster too...

other than the case js like narf03 said, your opponent turtling n u can't find any hole to break into his base...then u'll consider broodlords due to their long range...