2
That is controlled by your theme, which quite often assumes that there will be a left block area.
You can do this:
1. Open the theme.html of your theme in your favourite HTML editor
2. change this code:
<td id="leftcolumn">
<{foreach item=block from=$xoops_lblocks}>
<{include file="default/theme_blockleft.html"}>
<{/foreach}>
td>
to
<{if $xoops_lblocks}>
<td id="leftcolumn">
<{foreach item=block from=$xoops_lblocks}>
<{include file="default/theme_blockleft.html"}>
<{/foreach}>
td>
<{/if}>
3. Upload to the webserver
4. Enable "update module templates from themes/yourtheme folder" in system admin -> preferences -> general settings
5. See if the theme is as you want it
6. If yes, disable the "update module templates..." setting again. If no, go to item 1 and try again