The advantage of allowing tomestamping in any curtom window by window basis via a switch is that it can be enabled as required, without applying it to all, and most importantly, if implemented in the same manner as for /echo removes the dependaancy of $timestamp on the requirement of a time stamp format to exist.
Consider the documentation for /echo regarding the -t switch -
The -tN switch prefixes the line with a timestamp if global time stamping is on or timestamping is on for that window. N is optional and is the UTC value to use for the timestamp.
In other words, no time format - no timestamp.
I still haven't used $timestamp without a format, but it will probably generate an error.