I don't think there's a fixed maximum. But every if statement means another calculation. Each nested if will mean more calculation time and ram usage and thus less performance.
The most convenient work around for the end user is to calculate the dimension as a field in the script. The most convenient short term work around for the developer is to tell the user to get lost. But in the long term that may result in unemployment.
Also with 80+ nested IFs, there is no dramatical loss of performance on the particular application I am contributing to. Also, I have no access to scripting in this context.
