A Simple Answer for the Inexperienced All-Grain Brewer
BIAB is a method of all-grain brewing that due to its quality, simplicity and economy, enables an easy skip from the often uncertainty of kit or extract brewing, straight into the delights and certainty of all-grain brewing. (You can forget about extract twang, steeping and partial-mashing or saving up for a traditional rig.)
BIAB not only produces beer equivalent in quality to traditional brewing techniques but also...
1. Is cheaper - BIAB needs less equipment than traditional methods.
2. Is simpler to do - There are several less steps in BIAB.
3. Is easy to understand - BIAB requires less terminology
4. BIAB takes less time - Less actual as well as, "hands on," time is needed in BIAB.
5. Needs less space - BIAB is ideal for those with limited brewing and storage space.
6. Is flexibile - Temperature steps, maintaing mash temperatures, brewing exotic beers are not only possible with BIAB but usually easier.
7. Uses equipment that remains valuable to all brewers - All the gear used in BIAB can be utilised by all types of all-grain brewers. The reverse is not true.
Unless you inherited a traditional brewery, it is very hard to think of any situation where BIAB is not the ideal set-up in both the short and long term. (see When Shouldn't I Consider BIAB?