Do you mean that you can hot-plug usb devices and use them in pd without restarting it ?
From:
"Ingo" <ingo@miamiwave.com>
I'm reading out the connected MIDI interfaces upon connection by monitoring 
the /dev/ folder with [hcs/folder_list] every couple seconds.
Whenever a new midi device gets connected I use a [shell] with [aconnect -i( 
to read out the names and IDs and send them with the midi input number of Pd 
to an lcd display while connecting it to the Pd MIDI inputs.
So whenever I connect a midi device I know where it comes in.