The electrification of transportation, driven by environmental concerns, has given rise to shared autonomous electric vehicles (SAEVs). Integrating SAEVs with Vehicle-to-Grid (V2G) technology, enhances grid stability and energy management. Unlike privately owned electric vehicles (EVs), SAEVs are managed by fleet operators who ensures that the vehicles are strategically positioned to meet immediate transport demands and longer-duration charging and V2G operations. This paper highlights key distinctions between EVs and SAEVs in V2G systems and offers a detailed analysis of SAEVs' unique features that enhance their role in V2G integration. Their coordinated fleet dispatch minimizes idle time, maximizes V2G participation, and ensures optimal energy distribution more effectively than conventional EVs. However, SAEVs pose greater operational challenges due to connectivity, reliance on public charging hubs, and the need to balance transport services with grid participation, while EV participation in V2G is highly dependent on user willingness. This study reviews control strategies and optimization frameworks for managing EV and SAEV charging and discharging, addressing key objectives, constraints, and uncertainties while highlighting their differing requirements and interdependencies. It further examines the benefits, challenges, and mitigation strategies for V2G integration, providing key recommendations for future research and development in this sector.