What are the disadvantages of keeping different type of expenditure types in 1 work pack

What are the disadvantages of keeping different type of expenditure types (budget elements like material, labour, subcontract etc.) in one work package? It is difficult to measure the performance of dissimilar budget elements. The earned value for all elements is calculated based on % completion, even if one of the element is not scheduled to start at the time of statusing. Thoughts?

I suggest you set up multiple WBS, so materials have a code, say XX1, labour can have a code XX2, then it doesnt matter what work package they are under, its just another method of sorting and reporting. In this way you can report overall progress of the work package, and separately report % complete for materials overall, materials within the work package etc etc. This is the way I have set up controls for years.....client WBS, internal multiple WBS, discipline WBS Area WBS.