One benefit of having an IP Iteration every PI is that it creates an estimating buffer for meeting PI objectives. PI objectives are a set of SMART goals that align the teams and stakeholders to a common vision and mission for the upcoming Program Increment (PI). They are derived from the business context, priorities, and dependencies, and are agreed upon and committed by the teams during PI Planning1 However, since PI objectives are based on estimates and assumptions, there is always a degree of uncertainty and variability in the delivery process. To account for this, SAFe recommends that teams reserve 10% of their capacity for each PI as an estimating buffer. This buffer is used during the IP Iteration, which is a unique, dedicated iteration that occurs every PI and provides dedicated time for innovation, continuing education, PI Planning, and Inspect and Adapt events2 By having an IP Iteration as an estimating buffer, the teams can improve the predictability and flow of value delivery, as well as reduce the stress and pressure of meeting the PI objectives23 (Must be taken from SAFe 6 Scrum Master resources) Reference:
PI Objectives - Scaled Agile Framework
Innovation and Planning Iteration - Scaled Agile Framework
SAFe Scrum Master Course Outline

One recommended practice for Scrum Masters/Team Coaches when coaching teams on presenting a draft plan at PI Planning is to align on how the team will answer questions about their proposed objectives. This practice helps the team to prepare for the feedback and input they will receive from the business owners, product management, and other teams and stakeholders during the draft plan review. The team should agree on who will present the objectives, how they will explain the business value and technical feasibility, and how they will handle any objections or concerns. The team should also rehearse their presentation and anticipate potential questions and scenarios. By aligning on how to answer questions, the team can increase their confidence and clarity, and demonstrate their commitment and alignment to the vision and goals of the ART.
Reference:
PI Planning - Scaled Agile Framework
Presenting PI Planning Draft and Final Plan Reviews Virtually
SAFe Scrum Master/Team Coach - Scaled Agile Framework