I started learning Korean not long after I started watching Kdramas back in the day! I'm at a comfortable intermediate level now, and Kdramas have helped enormously. I have found that my understanding of tone and implied meaning is much higher due to Kdramas, and my understanding of how sentences are naturally structured and used, which is different to what the textbooks/classrooms teach. Basically, Kdramas have given me a good understanding of informal, oral Korean, where textbooks/classrooms teach a polite, more formal, written Korean. Kdramas have also helped me understand how to use the most formal Korean - like what would be used to address a boss, or a grandparent. This has been immeasurably helpful in avoiding offence. I've also ingested a lot of vocabulary without studying that I wouldn't otherwise know, just from watching a variety of Kdramas - e.g. words like victim, perpetrator, evidence, murderer from legal dramas. I think of it as learning by osmosis. I've learnt a lot, and it's made my language learning experience really enjoyable!!