The short answer is "it depends". Many variables determine how often you should inspect a racking or storage system. If we start with what the law says; "employers must ensure that a racking or stacking structure will not tip or fall causing harm"(I'm paraphrasing), then we need to follow the trail from "how do I ensure that my structure will not tip or fall?". There are applicable standards and guidelines in both the USA and Canada that the law references (allthough differently by province and state). Basically, those guidelines require a racking system to be validated by an engineer competent in the field of racking and storage systems. Any engineer's report or drawings will state that the system must be in "like new" condition or free of damage. So if something is damaged then you are violating the design parameters set forth by the engineering.
It is certainly not practical to operate a racking system that contains "no damage" at any given moment in time. So, the question of how often do you inspect is really a function of the rate of damage. And the rate of damage in our experience is a function of aisle size, throughput, and management. Small aisles will always result in more damage compared to the same operation with wider aisles. High throughput rates will result in more damage, in particular if night shifts are involved. Lastly, management plays a big role in terms of the culture of the operation. Quite often we can tell how much damage to expect during an initial inspection just based on cleanliness.
So what it comes down to is the employers display of "best due diligence". A high volume grocery facility will need a formal inspection, monthly. A medium volume white goods facility might be fine with semi-annually. Our approach is to not guess but base it on data. If monthly inspections consistently produce lengthy damage reports then that frequency should be maintained. If the reports are empty most months then perhaps quarterly should suffice. The data allows you to just rely on the math. I like health and safety walks as a team that take a few aisles every week and look for damage that is blatantly obvious. And follow those with a more formal inspection that occurs on a frequency based on the averaged rate of damage.