Yes and no. If your APs support 80MHz channels, they may end up using it. That could be a good thing or a bad thing depending on your environment. I personally never use auto, not for Cisco, Aruba, or anyone. I look at the RF in the space and decide if there is room on 5GHz for 40MHz and if not, 20MHz it is. I find there to be very few scenarios where 80MHz makes sense. The thing to understand is that 80MHz uses 4 20MHz channels. That will limit the availability of non-overlapping channels and make CCI a potential issue.
Here is a great read on the topic, from Andrew von Nagy: http://www.revolutionwifi.net/revolutionwifi/2013/03/safely-using-80-mhz-channels-with.html
Here is Meraki's info on it: https://documentation.meraki.com/MR/Radio_Settings/Auto_Channel
That depends on the environment. In high-density deployments it's recommended to stay away from wide channels due to it being harder to avoid co-channel and adjacent channel interference if you have less channels (which is a direct consequence of having wider channels). In most corporate environments 20MHz channels are used.
Definitely read the points about default channel width in the docs below: