Assuming you know the syntax - and the guy modifying the script after you also knows
There is always a trade off. I often do C code optimizing for others. Optimized C usually looks nothing like what you might think it ought to be -- things like Duff's machine, for example.
I always leave the old understandable stuff behind, buried in comments. For the next guy.
If ksh were truly simple to learn then why did HP(?) come up with keysh? ugh....
Don't get the wrong idea - I use ksh - but put things like expr in production code so it's maintainable. If you're doing so much string substitution that expr is a performance drain, then the code should be in C or perl, not ksh. I think.