The thing is, it really depends on how you use your AirPods. If you just set them down on your desk before bed and charge them once a week, a regular cable does the job fine and you're just throwing money out the window. But if you've got AirPods on you all the time and you're charging them several times a day, a wireless case is way faster - you just set them down, done. No hunting for the cable, no connector getting all gunked up, no hassle wrestling the cable into the port.
Honestly, it's mostly a friction thing. Wireless removes one tiny step that can be annoying if you're charging constantly. Then there's the practical side of storage too: a wireless case can sit anywhere since you just need a power outlet nearby, whereas with a cable you've gotta be right next to a power source. That becomes interesting if you move around a lot or if you're charging in different places.
If you're not someone who's always charging and you're willing to live with a cable, honestly just skip it. But if you're the type who stresses about having connectors lying around everywhere and just wants to set your stuff down and forget about it, it can really be worth it. It's not pointless luxury, it's just a small optimization that becomes useful depending on your day-to-day life.