Lazy evaluation in R postpones the evaluation of an expression until it is necessary. This can be particularly useful when dealing with large datasets or complex calculations. By delaying the evaluation, R optimizes memory usage and improves performance. It also allows for the creation of custom control structures, where expressions are dynamically generated and evaluated on demand.

Lazy evaluation in R means that expressions are not evaluated unless they are needed. This can lead to more efficient code execution and memory usage. For example, when using the 'if' statement, the 'else' part is only evaluated if the condition is FALSE, which can save unnecessary computation. Additionally, lazy evaluation is often used in conjunction with functional programming paradigms, allowing for the manipulation of unevaluated expressions as objects in R.