There are some regulations in bond pricing or international banking or stuff like that that require over 25 decimal places. IIRC, the best COBOL or whatever could do on the IBM 360's was 15 digits. The smaller, cheaper, and older 1401 business machines didn't have any limit. Of course, for nerdy financial applications, compound interest and discounting of future money would require exponentiation, which was damn-near tragic on all those old machines. So was trying to add or subtract 2 numbers that were using the maximum number of digits, but with a different number of decimal places, or trying to multiply or divide numbers that each used the maximum number decimal places, with the decimal point in various positions, and it was suicide-adjacent to try to evaluate any expression that included multiple max precision numbers in which both multiplication and division each happened at least twice.