If you're doing accounting, sure you would want ACID compliant database. There you have a limited amount of kinds of data to store with strict and rarely changi

If you're doing accounting, sure you would want ACID compliant database. There you have a limited amount of kinds of data to store with strict and rarely changing constraints. You can keep it on one big expensive server (plus backup) and it's better to bring the system down to allow inconsistency. However, for most web development SQL is seriously not good. You end up with hundreds of loosely coupled tables which constantly change their structure for new features. Half dozen of joins on every request. Hundreds of lines of SQL. Constant pain. And it's not like you cared so much for the consistency - if once a year three comments disappear from your web site, so what? And it's painful to make SQL multi-master. For (the most of) web development document databases are so much better. MongoDB is pretty nice because it makes hundreds of lines of SQL with ten files of code redundant - all per one complex document.