What is the impact of using excessive effective radiated power on a satellite uplink?
Why A linear satellite transponder has a fixed, limited total output power that is shared among everyone using the passband, and many satellites also use AGC that turns the whole transponder down when a strong signal appears. Running excessive ERP on the uplink grabs a disproportionate share of that power and can suppress everyone else's downlink signals. Standard practice is to use the minimum power that gives you a readable downlink, checking your own signal against the satellite's beacon or telemetry.
Watch out Commanding the satellite into another mode or rebooting its computer requires specific coded command sequences sent by the control operators, not just a loud signal; raw power does not trigger those functions, and it does not overload the batteries either since the transponder output is limited.
Never louder than the beacon: extra uplink power steals the transponder from everyone else.