Half levels for each sub factor are always available for use within the Compensation tool. They are designed so that you can evaluate a Job Class that does not meet all the rationale for a higher level but meets some of the rationale. Hence you can allocate the proper point value for each sub factor for a Job Class and thus allow for greater distinction in your evaluations. For some individual sub factors or entire Point Tables half levels are not used and can thus be ignored in the evaluations and Point Table sections throughout the Compensation Tool.
Some sub factors may have explicit half levels turned on as their is no ability for a Job Class to be between levels, for example in a sub factor "Experience", each half level may be split into 6 month intervals (0 to 6 months, 6 month to 1 year etc...) hence there is no in between evaluations for each Job Class. In this case the Half Levels should be turned on, and explicit definitions for the half levels should be provided in the appropriate Factor Rationale section (find more information about turning half levels on here)
During Job Evaluations you will have the ability to select half levels, individual lines of rationale that justify a half level evaluations can be explicitly selected within the Job Evaluation Wizard or Job Details sections as well.
See also:
Evaluating Half Levels