Against navy you need decent amout of arty and you will need to shield it or destros will just come and use direct fire on them and kill pretty easy
also since all missileships outrange t2 arty i think it is not woth to use t2 art agains sera/uef/aeon navy, more then that, cybran navy have no shields, so you may use t2 arty agains cybran navy
also seen t2 arty work well on wonder when every one already made t2 pds and started ecowhoring
also on any map you may try to counter t3 arty with t2 stationary arty if you have no other choise
Edit: basicly if you construct t2 arty and it will shoot somewhere at enemy long enought it will be a cost effective unit, and as closer it is to enemy base more cost effective it becomes, like on winter duel... remember Juicy vs Lu_Xun