Data Modeling by far the most important task of Business Intelligence/Data Warehousing projects based on approach. You can either follow Kimball approach or Inmonn approach. As per Kimball, dimensional data model are best suited for data warehousing due to amount of data, simplicity and ease and performance of the SQL queries on dimensional schema.
Dimensional data modeling requires modelers to know the business process, how business works, data needs etc. However technical aspect of data modeling requires modeler to know the best practices of data modeling, process, ways to handle various business scenarios in data model. Without the correct data model future requirement of data from data warehouse may not fulfilled.