To have high-precision altimetric measurements in near-real time for integration into ocean forecasting models (operational oceanography)
To continue Topex/Poseidon - Jason-1 time series, in order to benefit from data over a period long enough to study ocean long-term variations (including mean sea level variations), and decadal variations (decadal oscillations)
To have quality data nearer to the coasts, and over lakes and rivers.
Expected applications are also Topex/Poseidon and Jason-1's :
ocean study,
climate study, seasonal forecasting (including El Niño and such phenomena),
wind speed and wave height measurements, in real-time for weather forecast models, and over the long term (climatologies) for studies and model improvements,
better knowledge of the geoid, in combination with geodetic satellites (Grace, Goce),
Past missions 
