When I no longer need voice control I use Siri to turn it off (I have my voice control set to label all actionable buttons on the screen so I like to turn it off when using my phone via touch.)
I'm not visually impaired however I find voice control super useful when I want control of my phone and rather not use touch or in a situation where touch is impractical.
Whilst Siri is good for certain tasks it lacks the ability to control every aspect of the phone whereas voice control is literally a replacement for touch control.
By combining Siri and voice control I get fine grained complete control of every app when I need it, all enabled/disabled via my voice. Such a brilliant combination.
Apple's attention to this disability feature is incredible. I only learnt about it after a visually impaired friend showed me how it works.
I learnt that voice control/voice over is the reason most visually impaired people use iPhone due to Apple's dedication to building world leading accessibility features.