I found it pretty useful, but not essential. We live in a flat so there is a bit of a walk between car and home and it was great for that when you have loads to carry. Also useful if you're doing things like dropping off older child and won't be out of the car very long - babies don't like being moved between different things they are strapped into.
That said, sometimes we forgot or couldn't find the adapters, so we just balanced the car seat on top of the actual buggy seat, which works absolutely fine over a short distance if you're aware/careful that it could tip off and keep hold of it.
If you're looking at the bigger brands like Nuna, it's worth knowing that a lot of the car seat brands use the same adapters these days. If you look at the adapters and they are kind of shaped like a U, and/or the description says they take Maxi Cosi, Cybex or Nuna car seats then they will also take Joie, Besafe, Avionaut and the most up to date Britax models (but not older Britax seats). Whether or not it's officially listed, they're cross compatible.
I would say, don't expect your travel system to be the only buggy you ever need until age 3 or so. A lot of them have smaller seats and fit nicely up to about age 2 but look cramped after that. Most people also get fed up of the bulk and having to fold it in two parts so additionally purchase a more lightweight stroller once their baby becomes a toddler. I would then use the lightweight one if they were going to be in and out or for short trips where we didn't need much stuff, and the bigger tanky one if they were going to spend more time in it or we needed a huge basket to carry loads of stuff, small one might also be good if you need space in the car.