Classical yoga and the original yogic texts suggest letting all vrittis, including the vikalpa, go. Yogis are advised not to fall for fantasies and the trappings of one's imagination. Instead, one should try to dissolve these ideas, recognizing their emptiness through yoga and meditation.
Although controlled imagination and visualization may be beneficial for yoga practice and daily life, vikalpa is uncontrolled and random, the kind of disturbance of the mind that should be avoided. There is also a term for useful, controlled imagination - kalpana - and this is used for visualization and opening the mind and body, as well as for the removal of obstacles and perceived limitations.