Monoculars are perfect for applications where weight and size is an issue. A Monocular is typically small enough where it can be put in a pocket or a purse. Golfers use Monoculars like the Hawkeye that have built-in reticals to judge the distance from a pin. Monoculars with very close-focus viewing capabilities are favored by those with vision impairments or butterfly watchers.
Spotting scopes are similar to Monoculars but they are not pocket-sized. Mount a spotting scope on a tripod, and view objects at high magnifications.