These numbers are used by the optimizer when costing query plans. That can be for proc compiles, SQL statement compiles, triggers, etc. The optimizer uses a great number of factors and statistics to determine how many physical ios, and cache io's a query/statement will need. Then uses these multipliers (along with other stats) to give each possible query plan a "cost". The plan with the lowest cost is chosen as the ultimate query plan to cache and execute.
A very detailed explanation can be found in the product manuals, or some decent google searches.
Here are some starting points: