In Abrahamic religions it is common I believe to say thank you to God before a meal. This is a key difference between these religions and religions like Hinduism.

The thanks is to the object that has helped us in anyway. This stems from the base of Nature/Environment worship that religions like Hinduism are derived from.

All things in the Universe are seen as a manifestation of God or Parmatma (Supreme life force) than God as a third entity.

As to whether it is useful, it is upto each individual to decide for themselves.

Note: I am a practicing Hindu and we just finished this ritual at home last week, including saying thanks to my Laptop :-)