Hi- I don't want to put words in my Guru's mouth, so the following is just from my experience:
I believe in terms of blessings (jenang) and initiations (wang), the issue of commitments and sadhana practices depends on the guru. Traditionally, most jenangs do not have commitments in terms of a daily practice. They are just a blessing of the deity in order to establish a relationship. However, for wangs, there are usually commitments and practices. However, this again depends on the guru as well. Based on what I have heard from other teachers, when you receive the initiation AND oral commentary on the practice, you are then obliged to do the practice. This again, depends on the Lama.