Being an Apple fanboy and owning an Apple TV 4k plus several HomeKit compatible devices it is a no-brainer for me to define an automation like “if I turn on light A, also turn on light B” or “if the water sensor detects a leak turn all lights in the house red”.
This is so easy to set up in the built in iOS Home app, see “Create home automations with the Home app”.
However it seems to be impossible with the Google Home app or with Amazon Alexa. Both services seem to be fully focused on voice control as the only trigger and simple actions. E.g. “Alex, turn off the lights in the living room” or “Hey Google, play my favorite playlist on Spotify”. At least Google Home has some “Routines” that allow you to run multiple actions one after the other, but still those need to be activated by voice or by time of day.
So if you want to have some helpful “If this than that” automations with Google or Alexa you need to rely on the hardware vendors app or a third party web service like IFTTT.com.
The problem with the hardware vendors app is that it will only support the devices manufactured by the vendor itself plus maybe the ones from one to two important other vendors and you need to have a hub/bridge/device running in your home all the time that actually executes the automation.
The problem with third party web services is that it is just another place online where you have to share your credentials and give them access to cameras, microphones, TVs etc. and share your daily routines with those services (beside doing this already with Google or Amazon). Plus the fact the automations won’t be run in case the internet connection in your house is offline.