What are the four regulative principles and what makes them important?
There's a difference between chanting Hare Krishna and following the process of Krishna consciousness. Anyone can chant anywhere and anytime and get spiritual benefit. At the same time, any mantra is more potent when received from a teacher and chanted as part of a self-purification process.
Any formal training requires discipline. The same way that scientific experiments and manufacturing processes often require controlled environments to achieve accurate results, when we avoid things that reinforce our material illusion, chanting the Hare Krishna mantra can more profoundly enhance our natural, spiritual consciousness.
Initiated devotees within the Krishna consciousness movement vow to chant a minimum quota of the Hare Krishna mantra each day on beads. They also take vows to avoid 1) intoxication, 2) illicit sex, 3) meat-eating, and 4) gambling. These are commonly known as the "four regulative principles."