在wordpress中消毒和逃逸的时间和地点？

Question

I was reading about Sanitizing and Escaping in wordpress, but i'm not sure the best way to do this, should i do this at the beggining, when i obtain the user input..or i should do it every single time i want to use this data(inlcude when i use echo,etc). for example here

<?php   //variables
            $author = sanitize_text_field(get_post_meta( get_the_ID(), 'author', true )); 
            $link = esc_url(get_permalink());
        ?>
        <?php if($count < $pars_limit || $pars_limit==0): ?>
        <div class="col-md-<?php echo $col;?>">
            <div class="img-wrap">
                <?php if ( has_post_thumbnail() ) : // check if the post has a Post Thumbnail assigned to it. ?>
                    <a href="<?php echo $link;?>">
                        <?php the_post_thumbnail('full');?>
                    </a>
                <?php else : ?>
                    <a href="<?php echo $link;?>">
                       <?php
                echo '<img src="' . plugins_url( '/asset/images/default.jpg', __FILE__ ) . '" > ';
            ?>

here i satinize the varialbes at the beginning, should i do that again whith the echo's?? thanks!