The Beam usually sits in standby and uses approximately 6w when idle. You can switch it off if you wish, but like TV’s/Mobiles etc; the device is meant to be used in standby mode. You do not have to set it up again. You just have to wait for it to startup, similar to a mobile phone/tablet, or computer.
Sonos kit is meant to run in standby mode. As Ken says, you can turn it off, but you’ll have to wait whilst it re-initialises - the queue on the device is also deleted, so you’d have to set that up again, as well…..
There’s lots of kit these days that doesn’t have an on/off button - and many of those that do go into a standby mode, rather than physically disconnecting from the mains.
I’m pretty sure the same applies for Bose soundbars: no on/off power button as they are designed to be “Always On” in a standby, ready-to-use mode when not in use.