Hostile followers travel with the player

1. Summon a creature
2. Hit it 4 times to make it hostile
3. Go through a door or use a Guild Guide

In OpenMW the creature will travel with you, whereas in Morrowind it stays at the original location and will be friendly and following again upon your return. Same with followers from quests.

Also works with command spells, though in Morrowind hostile NPCs under a command effect remain hostile upon your return, but they can be commanded again and when it runs out, they're back to friendly.