It's only another line on the paperwork!
Besides,
Certifying the installation of a cowl, large or small a/c. Is not the same as signing a check completion card to say it is fitted. As has been said before it's about accountability. Who fitted the cowl, not is it there.
In the event the cowl detached a MEDA or whatever could establish the installer and investigate the reasons for the error. Without a signature for the installation the installer is unknown and COULD (I'm not suggesting that they would however) deny any knowledge.