People often assume sofas and loveseats are the same piece of furniture. Sofas in fact, cover all forms of couches and soft seating for the living room. This includes sectional sofas or just single sofas. Love seats are smaller, two seater sofas. The easiest way to think of it is with this logic; all loveseats are sofas but not all sofas are loveseats.
Loveseats are named such because they only have two seats. They are a lot smaller than a sofa width wise. They are great if you have a particularly small living room or want to have some sort of soft seating in another room like a bedroom. A full sofa in a bedroom will look out of place, but the smaller, more intimate loveseat works well.
Sectional sofas are great for big families or if you know you will have people over often. Everyone hates being the person who can’t fit on the couch and has to drag over a chair from another room and be singled out. Sectionals let everyone enjoy sitting together. They often can sit 5 or more people.
If you have a pretty average sized home and a small family, a regular three seat sofa should be just fine. Add an extra lounge chair to give a few choices in seating.