Hi Erika (I was on the young parents chat thread that withered away! I was thinking of restarting it) - how are you doing?
I'm not going to answer your question exactly, as I think others will be able to come up with lots more health benefits etc than I could, I just wanted to share what I thought as it was a bit of a strange one for me.
Basically when I was pregnant I knew I wanted to breastfeed, it seemed natural to me as all my family had done so, however I had never known anyone breastfeed past a year and didn't really know you could, I think I just assumed the baby would self wean at that point.
Then I started to spend a lot of time on parenting forums (not MN - I only discovered it when DS was 3 months old) and it entered my consciousness that some people did feed toddlers as well. But (I am ashamed to say!) my first impression of this was that it was a bit weird and/or disgusting, when the baby was acting more like a toddler ie talking and/or walking.
Then as I came to spend more time on the boards, especially AP type boards, I read more about it and came to see it as a good thing, especially the idea of self-weaning which I think is the most natural and gentle way of doing things (which is my sort of philosophy, as far as is practical) and I felt worried because I still had this feeling that nursing past babyhood was somehow "wrong", and I didn't know whether I would be able to do it, but I wanted to do the best for my child. The only advice that anyone gave me online was that it's not like you breastfeed a baby and then breastfeed a toddler, they grow slowly and you don't really notice and it's just a continuation of the nursing relationship that you have had since the beginning, which I still didn't really find reassuring.
So my baby was born and breastfeeding went really smoothly and I mostly put it to the back of my mind but I still worried about it a bit, and then when DS was about 3 weeks old I met my NCT teacher at the class reunion and I mentioned to her how I felt about extended breastfeeding and she said that feeding a toddler is nothing like feeding a 3 week old, and that I shouldn't worry about timescales but just go with my current feeling (ie not say "I will feed to age 2" or anything, just say "I will feed until I or DS don't want to any more" and that by the time they are that age it's just a feed at bedtime and maybe in the morning, in bed. And that made me relax a lot and I realised I had this image of breastfeeding a toddler being like breastfeeding a little baby, in that you have to do it all the time wherever you happen to be - and it's not at all like that.
Anyway, (sorry this is a bit of a novel...) DS is now 14 months and I am still feeding him. I won't lie and say that it's perfect and wonderful and easy, because all my NCT friends have stopped breastfeeding now and he is still a milk monster and has got to the age where he likes to pull at my clothes to ask for milk, which speaking to a few people, is the "image" of extended breastfeeding which people don't like - and thinking back I was probably like this too, even though I don't mind him pulling at me when we are at home alone - and I've become very self conscious when around certain people about it, when I would just feed him anywhere and everywhere when he was younger. To be honest I think it's partly because of his fondness for milk over solid food, so that part depends on your baby, but I would love for our nursing relationship just to continue at bedtime and in the morning - I am thinking of introducing a cup of cow's milk during the day and hope that will reduce his need to feed so much.
So, er... in summary(!) - it's really different to feeding a 7 week old and it's really hard to imagine right now. Don't stress yourself out with "targets" to feed to, just go with the flow.
Oh and they don't need teeth to hurt if they bite you But teeth aren't that much of a problem. I find DS feeds a bit uncomfortably for the first few days after a new tooth comes through but he has never broken the skin. He has bitten occasionally but you learn to anticipate it. If they clamp on, there is a spot at the back of the neck which releases the jaw painlessly if you press it.
Good luck!