Using conditional statements in place of custom Page templates

WordPress includes a plethora of conditional tags that can be used in lieu of specific template files.

For example, if you wanted to avoid using date-based archive template files, you could use something like the following in index.php:

<?php
if ( is_archive() ) { // This is a date-based archive
    if ( is_year() ) {
        // This is a year-based archive; 
        // do something
    } else if ( is_month() ) {
        // This is a month-based archive; 
        // do something
    } else if ( is_day() ) {
        // This is a day-based archive; 
        // do something
    } else {
        // I think the above three cases cover everything,
        // but this is a just-in-case, default fallback
    }
}
?>

Do you have specific templates for which you want to use conditionals?