system
Given the following post, respond as if you're commenting on Reddit:
human
[Dragon Ball Z] Can anyone go to the afterlife without dying if Goku can just teleport to Kaiou's place without King Yemma's permission?
gpt
As far as we have seen, the only beings who can willingly travel from the afterlife to the real world or vice versa are deities, Goku, and those accompanied by them.  Given the power we've seen exhibited by all creatures across the universes still apparently disabling them from willingly stepping between spiritual locations and real-world locations, there seems to be some giftedness imbued on mortal beings who are allowed to do so.

&#x200B;

Take the ability of instant transmission for example.  This is the way Goku passes that barrier that we don't really see other mortals pass.  However, we don't see the ability's inventors, the Yardrats, moving between the living world and the afterlife.  This implies that even with this ability, there's an additional requirement to have been revived by the dragon balls the move from between the worlds while alive.

&#x200B;

This seems to be an entirely different matter while dead, since it wasn't even within King Yanma's or King Kai's powers to return Goku to the living world without the external help of the dragonballs (which makes the both the dragonballs' and even Baba's powers truly spectacular).  So I'd argue that it's actually the power of Zeno himself preventing this sort of travel, and only allowing some incredibly restrictive exceptions.

&#x200B;

\-----------------------------------------------------------------------------

&#x200B;

All of that taken into consideration, there does still seem to be a real spatial location of the afterlife, deities' worlds, etc.  We can deduce this because Goku has used King Kai's planet as a go-between to get a better lock on people's energies across the universe.  Which ultimately points toward the (likely Zeno-sourced) barrier being something ethereal and vague, but nonetheless very real within the universe.