It depends entirely on how you like to travel.  Some people use a single larger carry-on bag and stow it in the overhead bin after removing anything they want with them during their flight (such as their phone, a book, a tablet, etc.).  The benefit of doing that is there is more room for your feet.  Those who travel carry-on only and don’t check a suitcase will likely want to maximize all allowable baggage and bring both a rolling carry-on as well as a personal item.