system
Given the following post, respond as if you're commenting on Reddit:
human
[Star Trek TNG] Why does the crew experiment on/with the ship's warp core while theyre exploring the galaxy, or even while people are onboard? Is that not seen as risky?
gpt
These tests don't come out of nowhere, they've been validated theoretically, in simulations, and in the laboratory.  Field testing is the last phase of a long process.  Eventually any new configuration must be tested out on a real ship.  Of course there is still some risk, but that's the nature of the job.  In the immortal words of Captain James Tiberius Kirk, "Risk is our business."

Starfleet has ample resources, but not infinite resources, they can't just keep an entire Galaxy class starship around for no purpose but experimentation.  Even if they could, it still wouldn't reflect real operating conditions since real ships see stress.  

The only solution, therefore, is to have a ship currently in the field which has the latest model system test out the new configuration.  The reason the *Enterprise* sees so many upgrades and tests is precisely because it is a top-of-the-line starship.  It's engines are new, as is nearly every other system, based on tests run on earlier ships.  The results impacted the design of subsequent Intrepid and Sovereign class starships.

The *Hood*, a veteran Excelsior-class ship, doesn't see these tests because that class has already been run through all these experiments and that ship has been upgraded as much as it can be.  Those tests were used to inform the design of the Ambassador and Galaxy classes.