The petitioner is the party who files the initial petition asking the Arizona family court for relief. In a dissolution case the petitioner is the spouse who files first. Being the petitioner carries no inherent advantage or disadvantage in the outcome of the case. It simply means you initiated the proceedings.

The petitioner bears the initial burden of properly serving the respondent and ensuring the case is properly before the court. The petitioner's counsel typically takes the lead in scheduling and case management in the early stages.

In some contexts being the petitioner matters for procedural sequencing. At trial the petitioner typically presents their case first. In modification proceedings the party seeking the change is typically the petitioner regardless of who filed the original dissolution.

There is occasionally strategic value in filing first in terms of establishing the narrative of the case from the beginning and ensuring the court is in the jurisdiction of your choice. But it is rarely determinative of outcome.