The USNA is a highly selective school. Like all highly selective schools, the Admissions Board asks themselves many questions about a candidate. On the topic of academic record, their questions boil down to two main themes. First, has the candidate taken the most challenging and rigorous courses available to her/him? Second, if the answer to the first question is yes, did she/he excel in them?
At most schools, AP courses are among the most challenging and rigorous. The more you take - and do well in - the more favorably disposed any Admissions Board will be to your academic record.