Dreadnoughts are commonly used in Class 5/6 w-space PVE.
They would be one of the most efficient ISK making though, comes with much risk.
It would take up to ~10 Billions ISK for the initial investment according to recent dreads prices and you can earn up to ~2Billions per hour with optimal conditions in solo.
Check ashy’s website, probably one of the most useful tutorial.
Other than wormhole PVE, dreads are usually not used in the PVE since they are too vulnerable to the gang.
They are also used for some level 5 missions, kill the npc carrier one. Fly in siege blap the carrier, fly out and back in at 0 with smart bomb carrier.
It is risky as siege imobolisation not good if organised gang is hunting you. 90% of random tackle will die to insane room dps from full fighter spawn.
You can also use them for any random kill the structure but carrier’s can do it without the siege risk.