These save files include missions that have already been completed as well as features that have been unlocked by other players. Using a savegame file, which can be easily found online, is one of the best ways to skip missions in GTA San Andreas on PC. So even though Rockstar Games does not have any such options that allow the players to skip missions, there are other ways to do the same.
Even though hardcore GTA fans are willing to spend countless hours in completing each and every main mission and side missions alongside, the casual gamers don't have the time to spend on all these missions.