When I had Kieran, I learnt that breastfeeding can be a contentious subject. One of the many debates centers on whether weaning should be mother-led or child-led. The former states that the mother should direct weaning, often starting with schedules and limits on time. The other end of the spectrum is child-led weaning, which states that the child should have complete control of weaning.
For a younger child (say, under 18 months or so, definitely under 12 months), I firmly believe in letting the child call the shots. Those numbers are purely my opinion, of course.
That being said, I also think that the debate over mother- or child-led weaning is a false dichotomy, at least when they're a little older. In some cases, this is due to other circumstances that make it more difficult for the mother to continue breastfeeding. For example, Kieran was still primarily breastfed when I fell pregnant with Charlotte. For one who haven't breastfed through a pregnancy, let me tell you that it wasn't pleasant for me. I didn't want to cut him off completely, but I felt like I was crawling out of my skin every time he latched on. So I started limiting the length of time he was on a little, and the decreased milk supply from pregnancy did the rest. I talked to him about it, and overall it was a smooth transition. Once the milk came back, he actually picked it right back up, though I found I had to again limit for my sanity (tandem feeding is great, but can be draining).
When Charlotte was 19 months, I felt no need to try to wean. I wasn't pregnant, and breastfeeding wasn't a problem, so I continued letting her feed. As she neared two, I did sometimes impose limits, mostly by asking her to wait a little if I was busy, and she could understand that. This is just to show that each breastfeeding relationship is a bit different, as are the other circumstances.
So what's my end take on this? I think there can be a balance between mother- and child-led weaning when the child is a bit older. This can be due to the mother being pregnant again (note: breastfeeding during pregnancy is fine, and I'm glad I have done this, but breastfeeding during pregnancy can be uncomfortable for some) or just needing a little more space. I think when done in a balanced way, where there is a lot of respect for the child's needs and wishes, too, it is ok. But then, I'm just hashing out some of my thoughts based on my experiences.