On Drupal 5.1, I have configured a computed field to create an alternative link to the node using an abbreviated title. I use the following two functions to set the value of the field and the display value:
$node_field['value'] = l($node->field_link_text['value'], 'node/'.$node->nid);
$display = $node_field_item['value'];
I then created a View which draws on the computed value. (This View provides a list of nodes matching the taxonomy tags of the current node, a "Related Links" list. But since the "link text" is used rather than the node title, the results fit more nicely in a block.) It works fine (so long as I have re-submitted the node after the computed field is defined -- this took quite a while to understand).
However, if I uncheck "Display this field", not only does the computed result not show in the node, but it also does not show in the block I have created to hold the View results.
Curiously, if I go back in to edit the computed field again, the "Display this field" box is checked, even though I had unchecked it previously. This made troubleshooting this problem a bit trickier.