In traditional production practices you know what you are aiming for. The scope is defined by the end product or result.
The journey to that end has discrete steps, a pipeline, which over time gets clearer and clearer, optimized for the ideal balance between time, effort and quality.
In art, and very similarly in science, the outcome is not known. It has a high chance of failure, of missing the mark, of wasting time and uncertainty runs through the whole ordeal.
Very often you find yourself with an end result severely (or pleasantly) different from the one you set out to create.
By focusing instead on process rather than product we can gain objectivity and creative freedom; the best features of experimental processes. In many ways the process IS the product.
If you vividly describe the outcome at the outset, you are fusing all of your assumptions and lack of knowledge with it; it is probably far from what you will end up with and it will in fact be worse from the burdens of your prior knowledge.
Knowing the outcome and process in this way for production is a vital and incredibly useful tool - more experience means more clarity, which means optimal performance and enhanced creativity within the confines.
Experimental process however, is a continual journey through the dark that does not stop when you come to the product or result at the end. If instead we consider the products simply as useful side-effects from the bullish execution of our experiments we free up creative capacity to see our progress for what it truly is.
If you don't have a destination, you aren't frustrated about getting it wrong, instead you're exhilarated at the shores of the new frontier you have discovered.