Although I am not a time trialist per se, I firmly believe in the importance of this type of training in a holistic program. For ALL the athletes I coach, I include these types of efforts. Only a select few would claim they are focused on time trials, however it is a critical type of tuning for your cycling engine. The physiological benefits at threshold are huge and the type of suffering tolerance gained is massive.
I personally dread these days. The monotony of setting your body at your threshold wattage and suffering for 20, 30, 60 minutes is my biggest enemy. My body craves speed changes, rest, and all out efforts. So I fight the urge to soft pedal or to just gun it for a minute and settle in to the rhythm of pedal stroke and breathing that I know is just on the cusp of blowing up, but not so hard I will.
Including these efforts in your early season riding is critical to creating a large book of matches to burn during races. These efforts also allow you to learn about your body and what threshold feels like. During a race, that knowledge is critical when in breaks, attacking, bridging, etc.
One word of caution, it is very easy to become over trained when including too many of these workouts. They can be hard to recover from and accumulate over weeks of hard training. So paying attention to the little signs of over training (HR compared to power, energy, sleep, etc.) is important if you are focusing a number of workouts on this type of training.