The prefix option is there to allow Aspell to easily be relocated. Changing prefix will change all directory names relative to the new prefix that are not explicitly set. For example if prefix was /usr/local/aspell and dict-dir has a default value of /usr/local/aspell/dict than changing prefix to /opt/aspell will also change the default value of dict-dir to /opt/aspell/dict. Note that modifying prefix will only affect the default compiled in values of directories. If a directory option is explicitly given a value then changing the value of prefix has no effect on that directory option.