Darśana-Śāstra is a serious act to do a philosophy. Acts something like kāka-danta-parikṣā or jala-tāḍana are useless exercise without any purpose, and therefore there has to be some purpose-prayojana. In the absence of intention even a stupid person won’t commence any activity.
प्रयोजनम् अनुद्दिश्य न मन्दोऽपि प्रवर्तते।
यावत् प्रयोजनं नोक्तं तावत् तत् केन गृह्यते ।
And all these systems were having vāda within and with each other. There are so many philosophical systems, and thats the beauty of different worldview and debate on the same text. So, the philosophical system which is called the Darśana-Śāstra is divided into two — Darśana and Śāstra. Darśana gives goal of life, it makes us realize and discover of what we are. Goal is of total transformation. Śāstra is the means of achievement of goals, it provides method, path and model to the world views.
तत् शास्त्रं पुरुषश्रेयस् अभिधत्ते।
सर्वो हि शास्त्रार्थः पुरुषार्थपर्यवसायी।
All system of thoughts ultimately must terminate in showing puruśārtha which is the ultimate goal of life. So, philosophy is to be done for a purpose.