No, it's the *type* that specifies which data is contained in the *value list* and graphing front-ends use the *type* to determine whether to label the vertical axis "bytes" or "packets", chose a fitting graph title, which colors to use, whether to stack multiple metrics in one graph of create a separate graph for each metric and so on. See https://collectd.org/wiki/index.php/Data_set for more information and further pointers.