When I see a pair of giant snips, I think of Laurel and Hardy. Snips do look a lot like scissors, but they tend to be large enough to make great props for a comedy routine. Maybe a Three Stooges skit is more like it: The scene would benefit from some of their inimitable sound effects.
More to the point, some pairs of snips are enormous, some are smaller, but all consist of a pair of blades that pivot at a center point. They are put to use like scissors, too, in cutting operations that slice through thin layers of material.
Snips are, by definition, metal-cutting tools. Compared to scissors, snips have disproportionately long handles, which provide added leverage when cutting metal. Some snips have ring-shaped handles enabling the tool to be held like scissors; others have straight handles. Snips can be used one-handed or both hands may be required, depending upon the weight of the tool and the gauge of the material to be cut.
Snips are indispensable for a variety of jobs. For example, in cutting flashing (metal used to seal off roof joints and angles to prevent leaks), using snips can make precise cuts of the aluminum or copper a simple matter.
Snips are manufactured with blades that have straight cutting edges or curved ones. Tight, concave cuts are made easily using hawk’s-bill snips, tools with blades in a crescent-like curve. More gradual curves are cut with blades that are curved more gently.
Unless you need to cut sheet metal frequently, the chances are that a single, smaller pair of snips will fill your occasional needs. One option I favor is a design called compound leverage snips. The advantage of their double-hinged design is that there is less force needed for cutting, which translates to easier, more accurate cuts. Compound leverage snips, which are also known as aviation snips (because they were developed for use in the manufacture of aircraft), can be purchased with blades designed for right-hand, left-hand, or straight cuts.
Another option is a pair of duckbill snips. Though unsuitable for cutting sheet metal of heavier gauges, duckbill snips are ideal for cutting screening, light-duty sheet metal, and wire. Because their blades are relatively narrow, duckbill snips can also be used for cutting gentle curves.
Whatever kinds of snips you use, never try to force them to cut materials that are heavier or harder than they are designed to cut. If you do, the blades will dull rapidly and create problems for future projects.