Good question! I’ve been completely happy with two bins plus a spotting scope for almost 20 years. A pocket (formerly an Ultravid 8x20, recently a Curio 7x21), a Swaro 8x32 EL, and a Zeiss 15-45/65. In order of most use it is the pocket, 8x32 and scope. Most lifers were seen with the 8x32, followed by the scope, and finally the pockets but I would not give up a good pocket bin for anything. If I was looking to add one more binocular, it would probably be a 10x42 or 10x50 just to get a little more reach and low light capability. I’m not really in the market but if I were to move someplace near the shore or with more open vistas, maybe. Some of the new wide, flat field are very impressive, but of course, expensive.