It is not a waste of time. Our prayers for the dead shortens the time our loved ones spend in Purgatory, which is an extremely painful place. It is painful to let go of attachments to sin, and it all happens there, if it does not happen during their lifetime.
When we pray for them at the cemetery between Nov 1-8, the Roman Catholic Church grants a plenary indulgence applied to the soul prayed for. A plenary indulgence frees them from Purgatory. It is quite hard to get a plenary indulgence though, as the person praying needs to be free of any attachment to sin, which is very difficult. And in this case, the indulgence is only partial. But the souls in Purgatory appreciate any shortening of their stay in Purgatory! They can be in heaven sooner!
So I pray for the dead, and unfortunately, the indulgence I can get for them can only be partial. The souls in Purgatory are extremely grateful, and they pray for those who pray for them. I encourage you to pray for your dead loved ones!
