We use SEMRush as a campaign management and competitor analysis tool for our SEO campaigns at TLo Ventures. While I believe you can use it for research into PPC campaigns and competition there, we mainly use it for the organic side of things. There are many features of SEMrush and we do not nearly use them all, but the ones we focus on are the Projects (for tracking keyword visibility, site problems, link tracking), and then the standard keyword/domain research tools like the "Organic Research" tab (for looking at what keywords a domain ranks for or what domains rank for a keyword). If you ever hear of a website or keyword and want to get some basic ideas of volume, competition, difficulty, etc, SEMRush is great for that.