Avantages
Advantages of a company include: it is a separate legal entity from the owners there is usually limited liability for the shareholders (unless they have given a personal guarantee); you may be able to take advantage of tax minimisation schemes (legal ones, of course!); it may make it easier to attract capital investment because of shareholders' limited liability.
Inconvénients
they can be complicated and expensive to establish and administer if it is a "large company"; if you are not a sole shareholder, the shares may be difficult to sell; if you have only a minority shareholding you may be allowed little or no input into the affairs of the company; you will only be able to leave the shares in the company to your beneficiaries under your will, not the assets of the company separately; and they require expensive procedures to comply with processes.