1. "Nursing makes the job of mothering easier, not harder." Norma Jean Bumgarner

This has got to be one of my favorite reasons. Of course, it's so good for the child but also what mom doesn't need her life to be easier?! The good old reasons like "it's always perfect and ready" still apply but with older babies and toddlers nursing becomes so helpful emotionally. The sucking reflex continues to be very soothing for children far past a year and let's face it, toddlers get upset kind of a lot. Whether they've scraped their knee or don't like the way their clothes feel, nursing will almost always help.

2. Emotionally Strengthening

Our culture tends to believe that the only way children will become independent is by being thrown into the water, but really the opposite is true, when we let kids reach their own milestones they conquer them courageously. When they're made to do things before they're ready, like weaning for example it can have a negative effect and make them more nervous and clingy.

6. Humans are meant to nurse longer than a year

The work of Kathy Dettwyler compares human growth to that of non-human primates. She reviews growth, birth weight, and dental growth with all cases showing that biologically humans should be nursing much past the age of one year.
"Based on these comparisons, an estimated natural age at weaning for humans would be a minimum of six times gestational length, or four-and-a-half years"

7. Mothers Risk of Illness Declines

The longer you breastfeed the more your risk of getting cancer decreases.
"Compared to parous women who had no history of lactation, a period of lactation of 13-24 months decreased the risk of breast cancer (RR, 0.7; 95% CI, 0.5-1.1), and this risk was decreased even further for those who breastfed for more than 24 months (RR, 0.6; 95% CI, 0.3-1.0). There was a clear trend of decreasing breast cancer risk with the duration of lactation (p for trend <0.001)." Effect of Lifetime Lactation on Breast Cancer Risk

8. Be a Badass Breastfeeder!

Adults and children need to see breastfeeding in everyday life and know that it is healthy and normal. Breastfeeding your toddler and beyond gives you a longer time to demonstrate your breastfeeding to the world and help normalize nursing.+

9. WHO Says?

Both The World Health Organization (WHO) and UNICEF recommend that women should breastfeed their children until they are at least two years old and that there are many health benefits in doing so.

10. Just Because!

Because you and your baby both love breastfeeding! You've made it past the hard part and your work has paid off. Enjoy it!

Along those same lines...
How do you know when it's time to stop nursing your toddler or child? Unless there's extenuating circumstances keep nursing until you or your child feels done. I hear from lots of mamas who are just kind of over it but their older babies are still going strong. Negative feeling from mom can only hurt the relationship so if you've tried your best and just don't have positive feelings about nursing anymore then you have arrived at the perfect time to wean!

Further reading:
What are the Benefits of Breastfeeding Mor more Than a Year? by Ann Smith IBCLC
La Leche League's Extended Breastfeeding page
Search "Extended Breastfeeding" on The Natural Child Project