Is it a good idea to use COLUMN AS (left([Another_Column],(4)) instead of LEFT in the select? I came across a table like this:

CREATE TABLE TABLE1
(
 CD1    int
,CD2    varchar(16)
,CD3    varchar(21)
,CD4    decimal(14,0)
,CD5    varchar(4)
,CD6    decimal(18,2)
,CD7    AS (left([CD3],(4)))
)


This table has more than 4 BILLION rows (totally unnecessary, but this is another topic).

As you can see in the last column, they use AS (left([CD3],(4))). I think this is pretty useless, since we almost NEVER have a SELECT on this table, and here is just using space.

Isn't it better to select that field during the select when needed?
If the computed column isn't persisted or indexed, it's only a virtual column (expression), and it's not taking up any "space".