The most important columns in the Cumulative tab are those showing call count ( Call# ) and number of times on the top of the stack ( Stack# ). Looking solely at the number of times a function is found on the stack ( Stack# ) can be misleading, because functions which are on the stack are not necessarily using up much processing time. However, functions which are consistently found on the top of the stack are likely to have a significant execution time. Similarly the functions that are called most often are likely to have the most significant effect on the program as a whole.
LispWorks IDE User Guide (Windows version) - 25 Nov 2011