This is essentially clarifying that the event officials can call for a re-weigh at any time and as such the builders should be prepared for that. With many events not weighing bots prior to every fight this makes it clear to the builder that they need to ensure that their bots are within weight at all times, whether or not the specific event requires pre-match weigh ins.
It may be worth adding that robots being actively repaired/modified will only be weighed upon completion of the repairs/modifications.
The other side of it is this is explicitly calling out that it's an official or judge that calls for a weight check, not any random competitor.