On Tableau Server, aliases may get wrapped. In cases where there are many leading or trailing white spaces, these white spaces do not get trimmed and can make the alignment look incorrect. In Tableau Desktop these spaces get trimmed, so the alignment looks proper.
For example, one might have a column header "office supplies furniture", with left alignment set.
In Tableau Desktop, the column header would appear as
But once the workbook gets published to Tableau Server, the column header would appear as