For the only reason that actually we have on the industrial market enough technology and tools to comply with all process using rotating machine, so actually just having a look to technology is not enough anymore.
And more than this if we build high efficiency product and we talk a lot all around the world of energy saving is not only for fun, but to push people working in technical business like ours to go a bit more deeper than just make something moving and more and more take care of energy saving.
Using DOL and by-pass system is maybe the cheapest way to make some application running and more than enough for many applications than a variable frequency drive (VFD) system. But you'll never make agree that a DOL system can get you full efficiency of each component of an application due to all mechanical and electrical matter that make you can't reach like the principle of chaos theory.
But for me now we must go deeper than just make it run and add value like cost energy saving and this for huge power application or small like servo motor application, maybe it's better to reduce a bit the speed and acceleration to have less big power drive and motor and have less power used or improve mechanical part of the equipment than oversize the motors, which is what most of the motor and drive manufacturer/supplier can do.
I'm not sure that softstarter, DOL and by-pass can permit to reach the full efficiency of a global mechanical equipment using electrical motors than a VFD. My meaning is that, it's not only energy saving that tell what to do, but the mix of application needs, technology that exist AND energy saving which is now something that we must ALL keep in mind to improve our solutions to our customer then to participate to all environment matters.