Some string-based languages (including but not limited to sed, Retina, ///) can't really handle integer arithmetic in decimal (or other normal bases). Therefore, these almost always have to start by converting the input from decimal to unary, and the output back from unary to decimal, which can easily outweigh the actual solution, which is often quite elegant.

Should (by default) unary input and output be acceptable for code-golf challenges dealing with integer input/output? (This default would apply to *all* languages, not just the string-based ones.)