It is preferable to give ( even paying clients ) and editor role instead of an administrator role. This way you can be in control over theme settings and plugin installations / updates. But there are some things you can a allow your editor to control that do not fit in the role capabilities. Two things I often run into are:

• Editting the menu
• Editting form settings

With the next code you can allow editors to edit forms and menus.

/**
 * Gravity and menu access
 */
function pud_add_form_menu_capabilities() {
    if ( get_option( 'pud_add_gravity_menu_access' ) != 'completed' ) {
        $role = get_role( 'editor' );

        $role->add_cap( 'gform_full_access' );
        $role->add_cap( 'edit_theme_options' );
        update_option( 'pud_add_gravity_menu_access', 'completed' );
    }
}

add_action('init', 'pud_add_form_menu_capabilities');

function pud_hide_menu() {

    if (current_user_can('editor')) {

        remove_submenu_page( 'themes.php', 'themes.php' ); // hide the theme selection submenu
        remove_submenu_page( 'themes.php', 'widgets.php' ); // hide the widgets submenu
        remove_submenu_page( 'themes.php', 'customize.php?return=%2Fwp-admin%2Ftools.php' ); // hide the customizer submenu
        remove_submenu_page( 'themes.php', 'customize.php?return=%2Fwp-admin%2Ftools.php&autofocus%5Bcontrol%5D=background_image' ); // hide the background submenu


        // these are theme-specific. Can have other names or simply not exist in your current theme.
        remove_submenu_page( 'themes.php', 'yiw_panel' );
        remove_submenu_page( 'themes.php', 'custom-header' );
        remove_submenu_page( 'themes.php', 'custom-background' );
    }
}

add_action('admin_head', 'pud_hide_menu');