I love using a carrier, but since I am often traveling & out & about alone with my DS (16 months) I have found the stroller essential, if only for 1 thing - using the restroom! I have used the RR with him in the carrier (once on the front, once on the back) but it is an emergency only situation...
Also, if you are shopping & ever need to try something on...
I had DS in the stroller when I was trying on bras in Fashion Bug (wasn't planning on shopping, Fashion Bug was right next door to grocery store & going out of business +70% off + 14 months PP & in desperate need of supportive (ANY) bras - still nursing...) and decided that he could play with his cars to stay busy while I tried on bras... Worked great until he realized that he could crawl under the door & escape! He was off before I knew what was happening (half naked woman running out of dressing room to capture escaping, delighted toddler.....) It got worse from there, after I caught him I turned the stroller on its side to block the space under the door, but then he noticed that I was topless & kept wanting to nurse... Nursing in front of a mirror is not recommended for this 43 year old Mom - I looked like something you might see in National Geographic.
So, to sum up, there might be a situation or two where you might want a stroller