Aside from aesthetics, why is it so satisfying to see green verdant pastures? A healthy pasture can mean a lower feed bill. Lush pastures also mean less soil erosion and manure runoff. The less land you have, the more management is needed to ensure your horse has healthy pastures.
In general, you need two to four acres per horse if you want them to be out all the time and not overgraze a pasture. Most horse owners don’t have this kind of space but with planning and management, one can do more with less. There is a caveat though, even with a high level of management, there is a limit to the number of horses the land can sustain.