Part of it is eating related, I like to keep track of things on a week-by-week and day-by-day basis especially while trying to manage losing weight while keeping intensity high.
Concurring with @Cary_Blackburn , I also like to have the KJ in preference of the kcals for caloric burn.
I use KJs more often during base phase along side of training load/TSS to make sure I’m not pushing too far into overtraining territory and that I’m also getting the nutrients (calories) I need. There is some research and metabolic testing such as Bjorn Kafka’s “aerotune” and Alois Mader’s research relating Vo2 Max and protein synthesis to determine how much stimulus (KJ) is needed to adapt and by determining how much overload one can handle.
For example, a rider with a 70 vo2 max may have the best stimulus at 12,000-14,000 kj per week. You can then backtrack and determine how many base hours are needed per week to get the best stimulus for this ride. If every base ride is 210w average, then they are riding at 750 kj / hour. So
12,000 / 750 = 16 hours minimum dose for base training, and
14,000 / 750 = 18.6 hours as the upper-end before reaching over-training territory (if done chronically – a training camp, for example may have more KJ). If the 70 Vo2 rider can’t get 16hrs they may need to add in 1-2 Tempo or SweetSpot rides to get the adaptation they are looking for. On the other hand, if the rider is at hour 15 of 18 in a week but already at 15,000 KJ, it may be a sign they need to cut back on intensity or reduce volume, or take it easy for a couple days before pushing too far… Of course, you can just use TSS and CTL, etc, but sometimes it helps to have another component.
Anyways, there are a few ways to use it. I personally like to see KJ as a “tool” for training load, nutrition, and even monitoring over time to see how your body and RPE handles KJs over a longer scale