Join our CAD community forums where over 25,000 users interact to solve day to day problems and share ideas. We encourage you to visit, invite you to participate and look forward to your input and opinions. Acrobat 3D, AutoCAD, Catia, Inventor, IronCAD, Creo, Pro/ENGINEER, Solid Edge, SolidWorks, and others.
It's difficult to answer your question without know which specific product/configuration you're asking about.
To summarize: The P2 platform contains the majority of CATIA tools. P1 products contain less capabililty and cost less. P3 products contains more capability, costs more, and are not required by all companies (ie: Composites)
I found the following on the IBM webpage:
The three CATIA V5 platforms (P1, P2, and P3) make it the most scalable solution for product creation. CATIA V5 P1 users benefit from PLM productivity in an affordable way with the security of potential growth. They can conduct associative product engineering based on CATIA V5 product design-in-context, product knowledge reuse, end-to-end associativity, product validation, and collaborative change management capabilities.
CATIA V5 P2 users can optimize their PLM processes through knowledge integration, process accelerators, and customized tools. They can drive generative product engineering based on the largest application portfolio. They can perform "design-to-target," extensively capture and re-use knowledge, and stimulate collaborative innovation.
CATIA V5 P3 users access the highest productivity for specific advanced processes with focused solutions. They can lead expert engineering and advanced innovation, relying on unique and very specialized applications that integrate product and process expertise.
The CATIA V5 world is fully scalable because the P1, P2 and P3 platforms operate on the same data model, methodology, and management schemes. By enabling users to install P2 applications on top of P1 seats and by standardizing graphical user interfaces across platforms, P1 users can immediately do collaborative design within their extended enterprise with P2 users and later grow with P2 and P3 platforms as their business grows.