Multiple Regression is a very useful way to gauge the impact of an aggregate of multiple input variables on a desired outcome.  Multiple Regression is also an excellent way to see which input variables exercise the greatest impact on the desired output (EUR in the above simplistic example).  In turn, the ranking of inputs provides a pathway to tweaking the most inportant inputs for improved results.  Also, a poor Correlation Coefficient (R-squared) suggests that there are important input variables that have not been considered.