I started oxygenating with my liquid pitches ~10 yrs ago. It had a huge impact on my beers' quality. I wouldn't think of pitching liquid yeast without giving the wort a blast of oxygen. YMMV. It's totally unnecessary with dry yeast.
This^^^
Studies on yeast and oxygen are numerous. They all come to the same conclusion.
Liquid yeast needs oxygen, it's not ever debated except among home brewers. It needs it to synthesize lipids for replication (cell membrane) and for producing sterols as well. I have talk to some homebrewers who stop using oxygen and have no ill effects, but then ask why there is an off flavor in the beer. I started aerating 12 years ago and the difference was tremendous, so much so that I would not brew without it. I enter a lot of competitions and I can't imagine I would win much without proper aeration, it's that fundamental. This is especially true for lagers. Some strains need more oxygen than others, but for the most part, lager yeast benefits from 12-15ppm of dissolved oxygen at pitch. The only way to reach that level is with pure oxygen through a diffusion stone.
Dry yeast on the other hand already has lipid and sterol reserves, so aerating at pitch is not necessary (unless they have been through a starter or are being repitched), but also not harmful.