It depends on the existing conditions of the roof and the leak itself. Once an asphalt roof reaches a certain age or condition and the elasticity is compromised, the shingles become brittle. At that point, an attempt to repair would be impractical. If the leak has been extensive then the sheathing may need to be repaired and could result in a replacement of the whole section of the roof plane. Each condition of a leak should be carefully assessed to assure a proper seal.