Considering that we have been hearing of the "blue wave" for the past several months, it was a milk success of sorts for the GOP, even if the Democrats took the House. If there is a silver lining, it's that the GOP further took control of the Senate, thereby all but ensuring that future judicial picks will get the fast-track to confirmation. I wouldn't be surprised if Trump got another SCOTUS pick, so the Senate is key in that regard. While the House can initiate investigations into Trump now, it's not as if the House under Republican leadership was getting a lot accomplished, apart from the tax break (though I suppose the gutting of Obamacare did get through, even if it failed in the Senate).
I guess the thing is that if House commences impeachment proceedings, it will drag on for a long time and make it hard for Democrats to have any other message. How much would that resonate with the populace? Are people going to be more inclined to vote for Democrat politicians in the future because they were anti-Trump? Will this make it more likely that a Democrat presidential candidate is elected? I don't think so. Everybody has a sense of what kind of person Trump is, so it's already reflected in the sticker price, so to speak. I think an anti-Trump push by Democrats will end up hurting them in the long run, even if it serves as "resister porn" in the short term.