This applies both to the magical objects one creates, but its far more than that. When working with spirits, learning to recognize them as finite beings with their own skills and lacks is incredibly important, as I have yet to find a spirit that does literally everything equally well.
Instead, there are gray areas and what amount to hidden footnotes within the body of Work, and only experience is really going to help you to ascertain the natures of these spirits and their skillsets. Learning this and then learning to apply this to your life and magical practice is an intensely rewarding experience, though its difficult as hell at first, as there's not really a well-established guideline to follow.
Learn to pay attention to these spells you do and spirits you work with. Jot down notes about the materials you use and how their inclusion affects the Works you do. There are an infinite number of subtleties that really cannot be adequately conveyed within the body of a blog post, so I invite you to experiment with this concept mindfully. ;)
Enjoy your Thursday.