Question
For a long slender structure similar to beams, propping is compulsory after elimination of formwork with reasons?

Answer
After concreting, time at which arresting of formworks has not been too long; or else it would affect colour of concreted structures. For long span concrete structures, while they have attained enough strength to support their self-weight, creep deflection could occur in these structures if propping is not provided after removal of formwork. So, re-propping is carried out after take away formwork and these props have not been allowed to stand also long since creep loads might overstress them.