This question was posed to me during a job interview.
This interesting question is from Pattern Fillets topic in section Pattern and Pattern Making of Casting-Forming-Welding I
The best explanation: Draft angles are normally included into the pattern design to make easy extraction of a pattern from the mould cavity. Draft angles are used in most of the pro¬cesses in which a pattern is withdrawn from the mould prior to pouring. Draft is very necessary to provide a clearance between the pattern and the mould during pattern extraction.