If you ever see wet or soggy areas on the tile bed it is time to investigate. Effluent will come to the surface if it cannot percolate into the soil, where it should be going. The reason could be that the tank is full of solids and a pump-out is required, there is a blockage somewhere, tile bed is saturated or the system needs to be repaired.
Keep your septic system healthy by adding the right kind of microbes, like the targeted microbes in EcoEthic Septic System Treatment!