Many BI vendors, particularly front-end solution-vendors, try to convince you that you do not need a data warehouse as a building or feeding mechanism for their front-end tool. This is a very bad advice and it will cost you dearly in the long run. These vendors mostly offer you to put together a quick proto-type for one single source of your ERP-system (e.g. sales) and they build a simple data-feed and trick you with a nice looking front-end result of your data and push you in a sale.