@BNI: If you want to stay happy as a Pistonpilot, learn and understand what the mixture knob does! I am very surprised you have training without intense teaching on how to manage fuel. Am I right, you have not gone through that part of the training were you scrub 15 traffic circles in 45 minutes?
Yes, it is indeed correct to point you to the POH, but it may be misleading as well. If you do training in an aircraft which was designed i.e. for 87 octane use and now fly on 100LL, the POH is not written for that and at latest, your FI should teach you what to do with the excess lead. If you drive an old 172 or 28 with TCM or Lycosaurus, you will get into trouble over time when not leaning on the ground -> thy collect lead on the sparks pretty quickly.