Hi all, I started the build phase program today and as a newbie to trainer road I wanted to ask whether ERG mode was the way to go on my smart bike?
I started the ramp test not on ERG but found it easier to switch it on and fight the resistance. My next workout though includes 15s intervals so wondering whether ERG would work well or not? Just curious of people’s opinions 
I wouldn’t recommend ERG mode for short intervals as there tends to be couple second lag in most trainers. For “longer” efforts do whichever you prefer
I’ve used ERG mode for every workout for 8 months. Not had any problems at all - even with short burts like Taylor and Spanish Needle. I only use resistance for extending workouts with z2.
For really those rapidly alternating intervals (like 15/15) I find it really distracting to shift the number of gears necessary to hit the targets in the timeframe required. In erg mode I have a hard enough time keeping my eye on the timer!
As it has already been mentioned there is plenty of material out there to help you out with this.
I will just give you my personal opinion.
For endurance, tempo, sweet spot, threshold and over threshold (until about 20 seconds of duration as a rule of thumb) it works great.
For sprint intervals not so much…
Also ERG mode allows me to push myself much more than I would otherwise because I can not reduce the power. I feel this is a great advantage from the physical conditioning point of view.
However, for tough intervals, mentally, at least for me, it can feel as when I am in a group ride holding the wheels for my dear life. In other words it does not give me the feeling that I am putting down the power and attacking the interval but rather that I am following fast wheels and hoping not to drop.
This although I guess teaches you how to suffer I feel is not the right mindset and is a bit of a follower vs driver question, but just purely on the mental side.
Hope this helps! Also, I am always willing to hear other peoples opinion.