The processes of disk evolution and planet formation are intrinsically linked. Protoplanetary disks around pre-main sequence stars play a central role in determining the physical and chemical conditions to form planets, while in return the feedback of the embedded planet(s) influences the disk morphology and contributes to its dispersal. In this picture, the sub-AU size inner disk corresponds to a transition/interface region between the outer disk and the central accreting star. A detailed understanding of the properties of these innermost regions is therefore essential to establish a coherent model of planet formation. Since 2017, the near-IR Gravity interferometer is operating at the VLTI and has been operated to conduct the GRAVITY Young Stellar Object survey aiming at exploiting the delivered milliarcsecond angular resolution to characterize the central regions of protoplanetary disks. We present here the summary of numerous results obtained on a large data set of high-, intermediate- and low-mass YSOs for which we measure the characteristic inner disk morphologies in the near-IR K band. Using the high-spectral resolution mode offered by GRAVITY, we explore the spatial properties of the hot hydrogen and CO gas in connection with possible inflow/outflow scenarios that are proposed to regulate the evolution and dispersion of protoplanetary disks.