The analogy method of estimating is frequently used to produce broad-brush evaluates at the start of a project. Why this method is mainly suited to such application?
Determining an analogous project on that to base calculates approximately does not need the detailed analysis and work breakdowns needed of other methods and therefore can be used to produce an estimate fairly rapidly. It is particularly appropriate at the start of a project while the decision-makers are probable more interested within knowing what 'ballpark' they are in, quite than having a correct computation of costs and timescales.