Usually(actually in almost all cases) - CHC will ask you eventually to prove your work experience through at least 2 sources. The more information you provide for your work experrience - the more genuine it sounds to them and your application becomes ironclad. They will give you options for multiple documents - employment contracts, employer reference letters, payslips, tax returns etc - but the burden is on you to convince them and hence the more documents you provide - the better it is for both you and them.
