Introduction
Extracts take up most of the space so minimizing the amount of data is key to reducing size and increasing performance. Generally speaking, if your extract is over 500MB you are probably doing something wrong.
Instructions
Workbooks by themselves are fairly small files. When extracts are used the data gets rolled in with the workbook when it is published and it can cause workbook sizes to increase dramatically. Aggregating extracts can help reduce file size and increase performance.
Filtering data as part of the extract will remove unneeded data/size and Removing unused columns reduces the size of an extract.
If the same data is used in multiple workbooks using a shared datasource makes sense as only one copy of the data is extracted onto the server. It also speeds up development and publishing.