How safe is keeping SATA disk connected without power?

[albert22]

Is there any risk in keeping the data cable for a SATA disk connected when its power cable is disconnected ?
There are several projects on the web to switch between disks by connecting them to individual SATA ports and switching on/off the power to one or more.
Of course the switching is done when the PC is powered off and never when the disk is in use.
But I wonder if the unpowered logic on the disk or the host may be damaged by doing that.

 

[tpetar]

If PC is turned off (motherboard is off, not standby state), then there is no problem to do that with HDs.

 

[albert22]

I mean that the disk will be connected by the data cable when the PC operates normally. This is to switch between disks with different operating systems. For example disk A is connected and powered on and disk B is connected but un powered. Then I could turn the PC off flip a switch and turn the PC on back again. with disk A no power, disk B with power.