Status Updates From Sanskrit for Seekers

How is learning ITRANS useful for a language where many of the letters are VERY RARELY used. For example - cerebral consonants - "All of the letters in this group are infrequent. If you encounter a word with a sound that might be in this group, it is for more likely that it will be in the next group" (i.e., dental consonants). I'll likely finish the book but focus exclusively on Devanagari going forward.