A simple explanation.
The "shot" (and "repair") button only need one click to launch attack (or repair all).
TACS includes an extra protection putting a overlay lock and you need one click to deactivate lock and a new one click to execute task, shot or repair.
Many times a click (accidentally) in "shoot" and I lost CP an RT. :-(
With this protection includes in TACS I saved many CP and RT. O:-)
Edited:
With the changes indicates by iguanaworld the overlay lock go to the correct coords over the two buttons of "shoot" and "repair". https://prnt.sc/qzexdm