A good reason not to use it is that 49::"char"::int == 49, but 49::"char"::smallint == 1. In other words, int casts directly interpret the value as an integer,

A good reason not to use it is that 49::"char"::int == 49, but 49::"char"::smallint == 1. In other words, int casts directly interpret the value as an integer, but smallint (and bigint) casts interpret it as an ASCII character, '1', which they then convert to the integer 1.