  Solar Orbiter provides unique capabilities to understand the heliosphere. In
particular, it has made observations of the far-side of the Sun and provides
unique information to improve space weather monitoring. We aim to quantify how
far-side data will affect simulations of the corona and the interplanetary
medium, especially in the context of space weather forecasting. We focused on a
time period with a single sunspot emerging on the far-side in February 2021. We
used two different input magnetic maps: one with the far-side active region and
one without. We used three different coronal models: a semi-empirical model
(potential field source surface or PFSS) and two different magnetohydrodynamic
models (Wind Predict and Wind Predict-AW). We compared all the models with both
remote sensing and in situ observations. We find that the inclusion of the
far-side active region in the various models has a small local impact due to
the limited amount of flux of the sunspot (at most 8% of the total map flux),
which leads to coronal hole changes of around 7% for all models. Interestingly,
there is a more global impact on the magnetic structure seen in the current
sheet, with clear changes in the coronal hole boundaries visible in extreme
ultra-violet (EUV) on the western limb. For the Wind Predict-AW model, we
demonstrate that the inclusion of the far-side data improves both the structure
of the streamers and the connectivity to the spacecraft. In conclusion, the
inclusion of a single far-side active region may have a small local effect with
respect to the total magnetic flux, but it has global effects on the magnetic
structure, and thus it must be taken into account to accurately describe the
Sun-Earth connection. The flattening of the heliospheric current sheet for all
models reveals an increase of the source surface height, which affects the open
and closed magnetic field line distributions.
