So say you want to set up a site with certain features like eg. forum Is it better to use free CMS and add forum plugin or get a specialised forum script (eg. vbulletin)? I would think the advantage of using CMS is that you can add tonnes of other features/functions by adding plugins in near future whereas with a specialised script it is limited to what it was written for
It really depends on what your needs are. None of the plugin scripts can match what a dedicated forum software can offer.