I started to save one space between - or + and a number, if a number is small, and my intention was - readability (not too much spaces, nor too less spaces). But of course when both operands are larger or variables, then I still use symmetric spaces.
And it's difficult to understand an operator as unary, if you have read one more operand in left side of an expression. DWIM doesn't work.
But ok, thanks for suggestions.