(Someone correct me here if I’m wrong but I think I have this correct).
Your fractional utilization is the relationship between FTP and VO2Max (FTP/pVO2 = fractional utilization)
If your FTP is 200w and your sustainable power at VO2Max is 240w, your fractional utilization is 83.3%.
In some cases, people push their FTP to a high fraction of VO2 (between 85-90%). This represents an opportunity to improve VO2 max (or in someone like Froome’s case, a rare genetic gift of efficiency).
Conversely, you can have a low fractional utilization (below 75%) which means that focusing on FTP is likely going to benefit you more, to being up closer to the normal range which is 75-85%.
IMO, a simple way to determine this is to look at the average power you can do 3-5 minute repeats at and compare it to your FTP. If you can do 6x3min repeats at 280w but your FTP is 200w, you would prob benefit from threshold workouts since your fractional utilization is low (200/280= .714 = 71.4%)
If your sustainable for VO2 work is more like 220w at a 200w FTP, you should probably focus on VO2 work instead, since you have a high fractional utilization (200/220w = .9 = 90%)