If it's not bitty and dragged out, yes. I've heard of systems where it's an hour here one morning, a whole afternoon there the next day, then lunch the followed day etc. That's confusing and unnecessary. It's also unnecessary to carry on for weeks on end like many schools use to, creating an absolute nightmare for working parents.
Three half days is not bitty and dragged out though. It allows children to get to know the new adults, the new setting and some of the rules and routines, plus some of their new peers, in a smaller group. It's the perfect balance in my experience.
All settlings are different so needs will naturally be different too. I've worked in a small village where all bar one or two came from the pre-school next door. They already knew us, from several interactions over our shared fence all year, and they all spoke English. They would have been absolutely fine to come in from day one full time. Where I am now it's a totally different story. We're up to 70% EAL (and some of those are very early acquisition). Due to cultural differences, some of them have never been away from their parents, let alone been to nursery. Some haven't even been in the country long. We take from at least 8+ different settings each year, in addition to the ones who have no previous setting. In those circumstances, even a few days does not feel enough but we do it to suit working parents.
Every year I see people on these threads claim a settling in period is unnecessary in their opinion or experience. Well their opinion or experience is very different to mine. As an experienced Reception teacher, I would always advise a short settling in period for the good of the children. There's no need to drag it out, but all children benefit from a initial smaller group if big changes to their routine are involved (ie they're not just moved over from the school nursery, with peers who already all know each other, adults they already know and a classroom they already feel comfortable in).
When children start nursery, they are offered settling in sessions. We offer the same for the exact same purpose, to settle them in. Yes we do some stay and play sessions for transition in June/July (slthough sadly I'm in an area where many don't engage with this, for whatever reason) but 6 weeks is a very long time for a 4 years old. They benefit from a few small group sessions in September before the new school becomes a full time reality.