BIAB is a great way to start brewing beer at home. If you have already been brewing from brewing kits or malt extract and boiling your wort then all you need to move up to 'All Grain Brewing' is the bag itself.
Customarily, home brewers who wish to brew from the raw ingredients have used a method involving three separate containers to create the wort which will be fermented into beer by the yeast.
The big advantage of the BIAB method is that only the boiler is needed. This reduces the expense, reduces the complexity and opportunity for things to go wrong and reduces the time taken to produce the fermentable wort. Additionally cleaning up afterwards is much simpler.