It’s for people who will never watch a cartoon mostly.
I agree it probably doesn’t make much sense to watch both. But I watched the live action show first (and I liked it) and then I tried watching a couple of episodes of the cartoon and I was underwhelmed; it looked kind of cheap and targeted directly to kids. YMMV, obviously.
The original series started airing in 2005 and was massively popular. My kids watched it religiously and we bought the DVDs of each season (plus it was well written enough to be enjoyable for parents as well). Those kids are in their 20s and 30s now, and while Avatar spawned an excellent spinoff series (The Legend of Korra) as well as a dreadful live action movie, there is a tremendous amount of nostalgia for the original; that’s why the live action series exists. Personally it exceeded my expectations, which were admittedly low going in after suffering through the live action Cowboy Bebop dreck.
Again, I watched the live action Cowboy Bebop first (and I thought it was OK) and then I tried to watch a cartoon episode and I found it unwatchably dull.
It’s definitely targeted at kids. It took me a few episodes to really get its town and start appreciating it when I first watched it (as a 45-year-old or so). But I would argue that the animated show is a much better kids show than the live action show is a… grownup show? Teenager show?
Part of the problem with the live action show is that it feels kind of stuck in the middle. It’s not grown-up fantasy. But it’s not fully for kids either.