If you have strong Riflemen, Ground Troops, Tanks, Artillery they can easily wipe out any base (along with the use of a good combination of tactics depending on the complexity of enemy base). So you will find that most people don't "waste" troop space on Wall Sappers.
Having said that, in unique circumstances you may require wall sappers where the walls are of very high level or double/triple walled (again dependent on the base design) - mind you, the wall sapper only blasts a wall only once, after that it's practically useless) . Even so, your levelled up troops, tanks and artillery can take down most designs. So again, little need for wall sappers.