sample Cell schema question

[jmlucjav]

In the sample schema.xml I can see this:

    <!-- Main body of document extracted by SolrCell.
            NOTE: This field is not indexed by default, since it is also
copied to "text"
            using copyField below. This is to save space. Use this field
for returning and
            highlighting document content. Use the "text" field to search
the content. -->
    <field name="content" type="text_general" indexed="false" stored="true"
multiValued="true"/>


I am wondering, how does having this split in two fields text/content save
space?