Should you use the Large Deformation "on", the FEM program will use another kind of tensor to solve your elasticity problem. As one colleage put it, if the elastic problem presents large displacements (NOT necessarily means large deformations), the it is geometrically NoLinear and the elastic equations require the use of a different simpler tensor relation. Hope this answers your question
Agree with Brian Ellul, if your problem is linear, it is okay, also it is not need to do that, but with longer computational times. If your problem is nonlinear, it should do that.