As seen online:
“Warp travel is the primary method of travel for almost all interstellar species in the Star Trek universe, and has no true viable replacement. Given how it's how almost all travel is carried out, the question arises of whether it's safe or not. In the year 2370, it was discovered that Warp engines were damaging the fabric of spacetime, causing subspace rifts. Captain Picard compared it to how walking over a carpet repeatedly will eventually cause enough gradual damage to wear it down. The temporary solution to this was for Starfleet to impose a speed limit of Warp 5 outside of emergencies, to try and reduce the damage caused to subspace. It was believed that lower speeds would cause less damage.”
— from How Fast Is Warp Speed In Star Trek? as of 23 February 2026