Panel building. Metric vs Calculation option at panel properties

Hi, i have a question regarding how to build panels - I am using Elasticsearch as a data source but i believe applies to any data source -. Lets say i am building a “Gauge” panel with an AVERAGE metric group by normal @timestamp. On the right side of the panel (Gauge properties) there is a CALCULATION option where i can choose from several options, MEAN, LAST (NOT NULL), MIN, MAX, etc. So the question is, what the idea of this CALCULATION option as i have already created my METRIC AVERAGE ? Thanks in advance. Regards