The Atheist Perspective
There is no god. If there were, you could have straightforward conversations with him whenever you wanted (and thus you could ask him this question, instead of asking it here). And prayer has no confirmed effects other than natural psychological and biochemical effects (such as placebo and anxiety relief), which is equally accomplished by entirely godless meditation.
Comments
Just because athiests cannot empirically prove this does not make it any less true.
Since you're the one claiming that god speaks and answers prayers, perhaps you could provide some evidence of this?