There are two events that I have observed that told me my long-held understanding of how to pace the bike in a triathlon, or’ Time Trial’, is correct.  The best way to describe this is you want to dish out the power in the most balanced way possible.  That power level is determined thru testing and is a topic I won’t cover here but here is another short description.  In a triathlon it is the power you should target that will also let you run to th3 finish at your potential.  

The first time I saw this rule being violated badly was watching the first IM in St George in 2010.  The bike course was like the WC last year but with even more climbing.  It had two identical loops up to Veyo with about 1,500ft of elevation gain over 45km each.  After about 38km you were entertained with just over a km of climbing at 8%.  I positioned myself on that hill to watch what happened when athletes went up the first and second time.  

On lap one the efforts were epic.  Quite a few were out of the saddle early on and for the rest of the climb.  I was at the top and could hear the respiration rate as the crested the hill, it was painful to listen to.  Lap two was just as painful looking for many and they were breathing hard but far fewer were out of the saddle for as long and going much slower.

I did that race the next year and again last year.   The last steep section did not require any out of the saddle work, with the right gears.

In 2017 an acquaintance was racing in Kona with me.  We had a similar swim split, he is 20 years younger, and we found ourselves riding together about halfway to Hawi on the rolling hills near Waikola.  He would power past me going uphill out of the saddle, I would shortly pass him going down the back side.  We kept that up until the long haul up to Hawi where we lost contact.  If I remember correctly, I had a modestly faster bike split at the end and a significantly faster run.  He had been trained by a coach I know well who would have never advised him to try and kill the hills.  He was working so hard going up that he had nothing left to power over the top, which is what I was doing, and catching him.

If you believe in the guidance given, I think by all coaches to keep the power in a very narrow zone its easy on a flat road.  It should also be easy on a steady uphill course, even if there are several downhills as well.  The hard course is one with lots of short rolling hills.  The kind that has just enough uphill to significantly slow you down without a lot of unadvisable high-power effort.

My strategy with the rolling hill courses is a modification of the rule being discussed.  This is very much dependent on the race distance.  In an IronMan I follow this idea very carefully; in a sprint I almost ignore it.  The trick is figuring out how many matches you can afford to burn over the distance.

Here is how I deal with the down and uphill at the north end of Boulder on Hwy 36, It is part of many triathlons in Boulder ranging from sprints to 70.3 so I know it well.  It comes after a steady 5.5 km climb with an average grade of 1.7%.  I try to keep the power just a bit over my goal power for those 5.5 km.  As I get close to the top, I start breaking the rule, in a sprint I would be in Zone 5 for about 30 sec to get going downhill fast.  In the middle of the down I would be back at my target power.  As the road flattens out, I put the power up again to maintain speed until I get to the meat of the next climb where I back off a bit to allow me to push hard over the top.  

The only way to figure out how many and how big a set of matches you can burn, without ruining the rest of your race, is IMO to find a route that approximates your upcoming race, or ride the course, as I can.  Indoor training Apps like FuilFGaz and Rouvy can help if you can’t get to the course pre-race.  The magic of us humans is we are all so different.  Simply doing a time trial to determine your Functional Threshold and then applying some rules is a good start but it is not enough.  

Training Peaks has a metric to help determine how good you are at keeping the pacing smooth, their Variability Index. (VI).  

VI is just what you might think it is, it’s the amount of variation in your power output over a period.  Training Peaks formula is.  the ratio of your Average Power to what they call Norm Power.  Norm power is another formula of theirs that is a bit more complex.  The easy description is its "an adjusted (normalized) average power for a ride or segment of a ride that accounts for the increased physiological cost of varying the power demands for hills and wind”. A VI of 1 means that the average and norm power are the same, easy on a flat road with no wind.  They suggest a target range for a Triathlon on a flat road is 1.00-1.04, and hilly course 1.00-1.06, not much more variation.  You might think you can’t do that on a hilly course but you would be mistaken.   Most of us can with the right gearing on a course that’s not extreme.  Even on the St George course last May my VI was only 1.18, that was an extreme course.  

For some more information take a look at this article from Training Peaks
https://help.trainingpeaks.com/hc/en-us/articles/204071734-Variability-Index-VI-

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