What is an example of an alloy how does its properties may make it more useful than a pure metal?

Possibly the best example is bronze, an alloy of copper and tin.

Both copper and tin as the pure metals are relatively soft, and do not hold an edge. As an alloy, as BRONZE, tools made from the mixture are hard, and hold an excellent edge. Most of the metals we use are alloys.

Steel is another good example, an alloy that contains up to 1.5% carbon, and its modern usage is ubiquitous in tools and structures. Brass is an alloy of copper of zinc. Other than its main purpose (which of course is to make musical instruments!), brass is used for gas fittings in that you cannot make a spark from hitting brass metal together (sparks in gas lines could be disastrous; why?).

Duraluminum is a mixed alloy of aluminum, copper, manganese, and magnesium, and being lightweight (because of the aluminum content), is used for manufacture of parts for aircraft.

There is usually a specific alloy to deal with a specific purpose. These alloys are purpose chosen by metallurgists to fill a particular niche.