I assume that's why they restrict its use now, because the overhead of repair/stress isn't worth the 2% thrust.
During WW2 there's a good chance they had no idea what they'd be up against whilst they were developing this jet, so they built in a theoretical 2% improvement switch with a large caveat incase the 2% improvement ever gave them the edge.
I think the use of the VMAX switch is only warranted if the ship would otherwise be destroyed or lost if it were not used, which seems like a very unlikely scenario.
Reminds me of how the Space Shuttle Main Engines gained improvements over time so you could then set them to 104.5% thrust. Higher modes were later available. From Wikipedia on RS-25 engines:
- Block IIA (RS-25C): First flown on STS-89, the Block IIA engine was an interim model used whilst certain components of the Block II engine completed development. Changes included a new large throat main combustion chamber (which had originally been recommended by Rocketdyne in 1980), improved low pressure turbopumps and certification for 104.5% RPL to compensate for a 2 seconds (0.020 km/s) reduction in specific impulse (original plans called for the engine to be certified to 106% for heavy International Space Station payloads, but this was not required and would have reduced engine service life). A slightly modified version first flew on STS-96.
- Block II (RS-25D): First flown on STS-104, the Block II upgrade included all of the Block IIA improvements plus a new high pressure fuel turbopump. This model was ground-tested to 111% FPL in the event of a contingency abort, and certified for 109% FPL for use during an intact abort.
During WW2 there's a good chance they had no idea what they'd be up against whilst they were developing this jet, so they built in a theoretical 2% improvement switch with a large caveat incase the 2% improvement ever gave them the edge.
I think the use of the VMAX switch is only warranted if the ship would otherwise be destroyed or lost if it were not used, which seems like a very unlikely scenario.