Not on smartphones, I guess (I don't have anything to compare it to -- never had an iPhone or Windoze phone).
But on the Lenovo Chromebook with 4Gb of RAM and a 2-core 1.6GHz Celeron CPU that I'm using as my desktop machine, it was slowing everything down.
You'd think it would only use resources when you were, you know, running Android apps. But nooooooooo, unless you uninstall the Google Play Store, there's always a bunch of Android crap running in the background.
Since I didn't have any Android apps installed that I couldn't live without, no biggie. But a machine that isn't supposed to need a lot of CPU power or RAM for most stuff can't have a bunch of extra CPU/RAM-intensive crap running on it all the time without getting a stomach ache.