The opening paragraph of a recent WA case says it all:

Home made wills are a curse. Occasionally where the assets of a testator are limited and where the beneficiaries are not in dispute no difficulties may arise in the administration of an estate.  Flaws in the will can be glossed over and the interests of all parties can be reconciled. But where, as here, the estate of the deceased is substantial, the will is opaque and there is no agreement among the beneficiaries, the inevitable result is an expensive legal battle which is unlikely to satisfy everyone. All of this could have been avoided if the testator had consulted a lawyer and signed off on a will which reflected his wishes.  There is no question but that engaging the services of a properly qualified and experienced lawyer to draft a will is money well spent.

Read Gray v Gray [2013] WASC 387 here.