The primary reason you want to visually inspect the enclosure and with a black light if needed is to ensure that you do not accidentally get stung.
You want to know exactly where your scorpion is before you put your hands on or in someplace that they could be. Most scorpions like to hide in the daytime in tight places. Some scorpions are quite small and can easily be missed, some because of coloring really can blend in with their hides.
Here is my female Buthacus Leptochelys Nitzani hiding in one of her usual hiding space. If i were to have just swapped out the Eva Dry without looking it could potentially mean me getting stung, her falling and getting hurt or her escape and none of those is good. I rotate out my Eva Dry every week to maintain a dry environment.
Remember simple precautions will make your scorpion keeping a pleasant experience.