In my experience both inside and outside it takes a lot of control to keep pressure on and hit targets. It is possible but takes control.
Here are some 30/30-sec intervals after 2 hours of riding outside:
so easy to take too much pressure off the pedals and lose control when going from on to off. Also had trouble controlling the switch from off to on.
Inside here is one of the best example of control on some 30/15-sec intervals (Brasted) on the Kickr with PowerMatch:
I’m actively pedaling and mentally engaged - that took a lot of concentration and control. Definitely not “I’ll just pedaling along at constant cadence and let erg take control” in fact the opposite.
I have examples of the opposite where I wasn’t in control.
Outside you can work on control, at one extreme are sprints with controlled recovery like this hit and miss effort:
7-sec all-out sprints with 1100+ watt peak power and I fought hard to keep spinning with some pressure at the end of the first sprint, but clearly gave up on the second one.
My point is - controlling power transition from to off-to-on and on-to-off is a skill. It can be done in Erg but its a bit weird and different than outside. IMHO you must practice outside, and inside using Resistance or Level modes. Over-unders are a good fit for working on this outside, or inside in resistance/level mode (or sim in Zwift).
Of course if you have a Kickr, turn on Power Smoothing and fool yourself into thinking you are a hero, the king 
of power control.