Redirect logged in users from the homepage to the activity stream.

buddypress-logged-in-user-redirect.php

<?php
function cfc_bp_profile_homepage()
//Redirect logged in users from homepage to activity. This happens after login or when a user tries to go back to the homepage.
{
    global $bp;
    if( is_user_logged_in() && is_front_page() && !get_user_meta( $user->ID, 'last_activity', true ) )
    {
        wp_redirect( network_home_url( $bp->activity->root_slug ), 301 );
        exit();
    }
}
add_action('wp','cfc_bp_profile_homepage');
?>