By far my biggest timesaver aliases are for cd-ing to commonly used directories.
alias ch="ch ~/Repositories/my_project/foo"
alias cn="cd ~/Repositories/my_other_project"
alias ch="ch ~/Repositories/my_project/foo"
alias cn="cd ~/Repositories/my_other_project"
(It lacks all of the magic of z -- it doesn't try to learn how you work. It's entirely explicit.)
However, I am wary of "smart" things that change with usage. I like my tools to be consistent and predicable. For example, I am constantly getting burned by alt-tab
That said, I imagine the "frecency" component of z makes it more reliable.