'Under the crazy presumption that a roll of duct tape has to exist somewhere on the Mars facility,' he wrote at the time, 'the Duct Tape mod sticks flashlights to your machinegun and shotgun. (Even if that means flipping the toilet paper direction in Fallout 4.) Though a number of modders developed solutions, the Duct Tape mod by Glen 'FrenZon' Murphy was the most popular. Whatever id Software's intentions were, if there's a demand, inevitably a modder will fill it. 'I love how you need to use your flashlight to move around and then when you turn in a room it highlights a monster all of a sudden and then you gotta run and switch to your weapon, it adds to the atmosphere.' 'The flashlight's separate use was designed for gameplay purpose,' wrote one Doom 3 player on the gaming message board NeoGAF, way back in 2004.
Other players saw it as a deliberate design decision to introduce risk/reward. Some folks thought it was annoying, irked by the burden of swapping between them.