  The Planck satellite is expected to improve the measurement of most
cosmological parameters by several factors with respect to current WMAP
results. The actual performance may depend upon various aspects of the data
analysis. In this paper we analyse the impact of specifics of the data analysis
on the actual final results. We also explore the synergies in combining Planck
results with future galaxy surveys. We find that Planck will improve
constraints on most cosmological parameters by a factor 3-4 and on the
tensor-to-scalar ratio r by a factor 9. Also inflationary parameters, like r,
n_s and n_run, are no longer degenerate. The tensor spectral index, however, is
little constrained. A combination of the 70 to 143 GHz channels will contain
~90% of all possible information, with 143 GHz polarisation information
carrying about half of the constraining power on r. Also, the error on r
degrades by a factor 2 if no B modes are included in the analysis. High-l
temperature information is essential for determination of n_s and \Omega_b,
while improving noise properties increase the l-range where Planck would be
cosmic variance limited in polarisation, with a significant improvement on the
determination of r, \tau and A_s. However, a sub-percent difference in the FWHM
used in the data analysis with respect to the one in the map will result in a
bias for several parameters. Finally, Planck will greatly help future missions
like LSST and CIP reach their potentials by providing tight constraints on
parameters like n_s and n_run. Considering Planck together with these probes
will help in breaking degeneracies between \Omega_K and \Omega_\Lambda or
\Omega_dm and f_\nu, resulting in improvements of several factors in the error
associated to these parameters.
