Here are my thoughts as someone who's been unfortunately Washington proximate for the last year or so.
There is genuine concern, among several groups, that the Trump administration's dogged determination to subvert political institutions means they'll bumble into something truly risky or catastrophic. Whether this is exposing US agencies to foreign influence or simply doing something so illegal that several other political projects will come undone or be sidelined by it, the risk seems higher than usual lately due to high turnover in the administration and a constant sense of not knowing who's responsible for what. For Democrats, this has obvious political consequences because it could prevent them from winning elections, but even among Republicans, there's genuine concern that they could end up over a barrel, particularly with an election coming up where they have some vulnerabilities. The impeachment inquiry allows everyone to take cover, including Trump. It allows for greater ongoing scrutiny that isn't contingent on Presidential authorization like the independent counsel was. An impeachment on the basis of electoral interference means Congress can work to limit or investigate various electoral manipulation scenarios meaning all of the campaigns will have to practice fairly strict discipline or risk political if not legal retaliation. It also sends a signal to would be interlopers that there's an investigative framework in play outside the Executive branch that has the ability to curtail foreign influence. This helps Trump because theoretically it means nations will be more cautious about running their own operations independent of him for fear of the resultant exposure making him actually lose. Assuming there is in fact "no collusion," the last thing the Trump campaign could possibly want is another attempted influence campaign being brought to light. The GOP meanwhile gets a respite from deeper inquiries into their own information campaigns and now has a vehicle to cut Trump loose if it really comes to that. The Dems get to mollify their left flank, maintain some degree of control over the electoral process, and try to salvage a floundering Biden by painting him as a victim of corruption. Pelosi also basically just handed a certain coalition within the party the future by giving them a wedge vote that'll likely become a litmus test in future primaries and national campaigns.
Everyone gets something out of this deal, including Ukraine, which will likely see all of its payments made on time going forward. The armies of bureaucrats, consultants and lobbyists in Washington will at least be able to breathe easy for a few months as things settle into a more predictably constrained pattern. And the big media companies, already drunk on the revenues this administration has given them, will basically be in a permanent state of orgasm.
This is political theatre, to be sure, but it's also an insurance policy. Also, there's the chance that this incident will be enough on its own to be taken seriously as a crime either in Congressional proceedings or in public opinion, which could disrupt some of Trump's already shaky political coalitions.
This process established rules of the road for 2020. Extrapolating its ultimate effects is fun, but mostly depends on rudimentary understandings of public opinion and intuitive leaps. The best we can reliably say is what this process does right now and for whom it does it.