Remember the van allen belt radiation is what spawned a lot of fake moon landing theories that suggested transit thru the van allen belts was not survivable with the limited/no protection that our astronauts had at the time.
If for example you built a space ship on low Earth with efficient but low thrust ion drive & wanted to take it to Moon or Mars, it would take it possibly months to slowly (but efficiently) spiral out to higher orbit and eventually towards its destination. Many of those months would be spent inside the Van Allen belts.
So for these mission profiles I have seen the suggestion of the ship being radiation hardened for autonomous flight & the crew arriving by a small fast craft only once it is out of the radiation belts.