Currently (8.5) when one wants to format a specific time other than "now" one has to write
clock format [clock add [clock seconds]]
Clock clock clock doesn't look very attractive.
Because tcl::clock::add already does a check on [llength args] % 2 it wouldn't be such a great hassle.
If uneven number of parameters is given, just
set args [lassign $args clockVal]
instead of erroring out, otherwise set clockVal to [clock seconds]. Would spare poor programmers brain to avoid clock clock clock, wouldn't it.