Let's say you want to process a list of numbers, a set of data records, or something fairly complex. Internally, you can pass it between functions in a fairly compact, but almost illegible form. If a human user wants to see what's getting passed around, though, it could be handy if the system could automatically transform it to smoothing more human readable: tabulated, indented, pretty-printed, what-have-you.
I could definitely see a use for this, strange as it might seem.
Having spent my life in networking tech, Tcl...please die.
TCL is an unreasonably effective language for certain use cases (the company we worked for were driven by extremely tight deadlines and high performance requirements (appserver written in pure C in late 90s, with call-outs to TCL for business logic).
I haven't touched TCL since, though.