Blind flange is put at the end of pipe or at the junction that would possibly be a future expansion into that direction.
Blind pipe flanges are often used for high pressure applications.
Piping is easier to drill or weld at the construction stage. Once it was in use, drilling or welding will need prolong cleaning especially when the fluid transferred is combustible. For the mean of future extension, either the blind or valve would be used to seal the end.
