Breastmilk after 6mth

I was told by my sis-in-law that i should stop feeding my LO breastmilk after he turns 6mth. She has 3 kids of her own; the oldest being 3.5yo. And because of this, my parents think she’s right and advised me to stop at 6mth also. What i read online was i could give my LO for as long as i could. Is the benefits really not there after 6mths? And i have plenty of frozen milk in my mini freezer, threw lots of bags to make way for new bags. It seems like i had been saving for nothing?