It'd be a public airing of evidence of trump's corruption, and would make a formal, condensed case, instead of the piecemeal we get, where 1/2 the people forget the last outrage because of the next one. Neither the news cycle nor regular congressional hearings lend itself to coherent narratives like an impeachment hearing does, where you have experienced lawyers presenting an actual case.
Unless you think the evidence somehow exonerates him, even though trump is doing his best to keep it all hidden, it won't look good for the president. The impeachment hearings surrounding nixon had the same effect that trump's will. I have seen zero exonerating evidence. It's all been inculpatory. This is where the idea that "it would be bad for democrats" falls apart. Trump wouldn't be stonewalling evidence that makes him look good. If the GOP fails to convict, the dems can literally run on the fact that the GOP is willingly allowing criminality at the highest levels of our government after a public display of evidence, where everyone would be able to see it and judge for themselves.