Set Case's Teams to the private team of the created by user and of the assigned user. This logic will work only if all users have as default team, their own private team only

afterSaveCases.php

<?php

// Enrico Simonetti
// enricosimonetti.com
//
// 2017-12-19 on Sugar 7.9.2.0
//
// Set Case's Teams to the private team of the created by user and of the assigned user. This logic will work only if all users have as default team, their own private team only
// file: custom/logichooks/modules/Cases/afterSaveCases.php

class afterSaveCases
{
    public function callAfterSave($bean, $event, $arguments)
    {   
        $GLOBALS['log']->debug('afterSaveCases->callAfterSave() for id '.$bean->id);
        $GLOBALS['log']->debug('afterSaveCases->callAfterSave() with team_set_id '.$bean->team_set_id);
        
        $teams_to_replace = array();
        $created_by_user = BeanFactory::getBean('Users', $bean->created_by);
        if(!empty($created_by_user->id)) {
            $created_by_private_team = $created_by_user->getPrivateTeamID();
            if(!empty($created_by_private_team)) {
                $teams_to_replace[] = $created_by_private_team;
                $bean->team_id = $created_by_private_team;
            }
        }
        
        if(!empty($bean->assigned_user_id)) {
            $assigned_user = BeanFactory::getBean('Users', $bean->assigned_user_id);
            if(!empty($assigned_user->id)) {
                $assigned_user_private_team = $created_by_user->getPrivateTeamID();
                if(!empty($assigned_user_private_team)) {
                    $teams_to_replace[] = $assigned_user_private_team;
                }
            }
        }

        if(!empty($teams_to_replace)) {
            $bean->teams->replace(
                $teams_to_replace
            );
        }

        $GLOBALS['log']->debug('afterSaveCases->callAfterSave() teams: '.print_r($teams_to_replace, true));
    }
}

install.afterSave.php

<?php

// file: custom/Extension/modules/Cases/Ext/LogicHooks/installer.afterSave.php

$hook_array['after_save'][] = array(
    1,
    'Cases after save hook',
    'custom/logichooks/modules/Cases/afterSaveCases.php',
    'afterSaveCases',
    'callAfterSave'
);