For all kinds of reasons, yes, a solicitor is necessary.
If you do not have a mortgage and you have your own title deeds, you could, amongst many other things, try drafting a watertight contract, drafting necessary Family Law/Planning Declarations, approving a draft Deed and satisfying a purchasers solicitor that you understood all that was involved.
If you have a mortgage, your lender will not release your Deeds to you personally unless you pay off your mortgage.
And if you are buying and you want to do a laymans job, then again you will need not to have a mortgage ( no way is a lender letting you acquire a property to mortgage to them without a solicitors input/insurance to call on) and you will need to know enough about title, drafting deeds, stamp duty, CAT, CGT, registration etc.,etc., to make sure you acquire a good marketable title.
There is a great deal more to conveyancing than changing the names and addresses on previous files!
mf