Custom metrics only allow the simplest of calculations (+, -, * and / ).
Where are the following common functions:
- Joining of Text and Text (or Text and Number) i.e. Concatenation
- Basic maths functions (log, square root, modulus, exponential)
- Conditional Logic (IF, OR, NOT, AND, Case/switch statements)
- Improved Numeric control (rounding, handling decimal places, etc) - some of this is covered here (Large Number Formatting)
- New Stats Constants (Summary metrics: average, row count, median, Standard Deviation, etc)
While, I'm sure that there could be many more additional improvements, these seem the most obvious when compared with other visualisation tools.