Well, other than say a 20 min FTP test? This article suggests that Erg mode might not be great for short intervals. I realise why, but I have never tried any workout without Erg mode.
Quote:
For ERG mode to properly kick in, you need to give it around 30 seconds. That’s usually the time it take most trainers to adjust and stabilize resistance. So I usually avoid ERG mode with intervals that are less than 1-minute in length. Usually Vo2 max or sprints, I like to disable ERG mode.
Complete BS.
Well, in short intervals, it does take a short while to build up sometime. At least when I am using powermatch.
30 seconds though? 5 tops on big stomps. (And I’m using the bottom of the range trainer).
Was thinking about it for Baxter the other day, purely so I could keep it in one gear and adjust cadence to hit target powers like the instructions say…in the end I didn’t bother but I might in the future for that workout.
I don’t recall any workout on TR starts with direct intervals. All workouts have a warm up duration where trainer adjusts itself. Then it really does not matter what you do,VO2Max or threshold or whatever, ERG Mode picks up the resısistance right away. It must be the legs which can not keep up with the required power output 
Bottom line:ERG Mode works just fine.
I’ve tried several times turning off ERG, I don’t like it
I switch to manual mode when I need to skip or bail on an interval, but I use ERG mode for all my intervals - including things as short as 6 or 12 seconds
I did this once recently and actually really enjoyed it 
Erg mode only, all the time. It feels like cheating. Especially with loud music.
I have never had my trainer take more than a few seconds (or less) to catch up with the wattage on TR. I have never turned off ERG mode, having used a dumb trainer for a few years before my Kickr.
I’d agree, 30 seconds is total BS.
No and no need to do so either!
I never turn off ERG - no reason to that I can see…I find that if I do turn it off I’ll end up zoning out at some point and missing the start of an interval. Additionally, I think the concept that ERG mode somehow decreases the training value because it adjusts the resistance automatically is nonsensical, so I just stay in it all the time for structured work (even for FTP tests now that I’m using the Ramp Test)
I guess I’m in the minority, but I pretty much always ride in “resistance” mode, never erg. This isn’t because of any lag–I prefer not-erg because I feel like it helps me practice what I need to do outside, in a race, etc.: trying to hold power on my own. My smart trainer still adjusts the resistance depending on the interval requirement–I notice this on the short sprints, in particular. But it is a different response than erg mode.
Erg 4 lyfe! 
You still have to work to hold the power on your own in erg. It’s not an autopilot where you can just space you, need to stay on top of it.
I did sixteen 5 second bursts in Ebbetts this week, and didn’t know what to expect. Was pleasantly surprised that it worked well in Erg mode on my Kickr17:
Erg mode off almost all the time. Unless it’s an easy recovery or endurance day.
I use resistance mode for low cadence, big gear work as well as for threshold and above intervals. I find it easier to hold higher watts in resistance mode. Erg mode for everything else though. I find erg mode slightly more fatiguing on the legs for some reason
ERG mode on the wahoo snap hits target power changes in < 5 seconds for me, love the zero shifting… Only problem is making it through 12 minute sweet spot intervals in ERG, no breaks 
