In large undergraduate science courses, instructors often invite students to voluntarily answer questions (VANQ) in front of the class for a variety of pedagogical reasons. However, it is unclear what drives instructor decisions to use this practice. We conducted exploratory interviews with 21 college science instructors from a research-intensive institution; some invite students to VANQ and some do not. We probed the perceived costs and benefits associated with inviting students to VANQ and participants' reasoning for why they implement or avoid the practice in their science courses. We found that instructors perceive that asking students to VANQ builds students' skills and knowledge. However, participants acknowledged that the practice could take away time from content delivery and potentially damage the instructor-student relationship. Instructors reported inviting students to VANQ for the purpose of maximizing student learning and avoided the practice to prevent an inequitable classroom environment. This study is the first to examine instructor opinions of and motivations for inviting students to VANQ.