Britannia was ultimately a net loss for Rome. Its sources of income should not be ignored, but the costs clearly outweighed the benefits. Now, if Rome had pushed through all the way, annexing Caledonia and Hibernia as well, that would improve matters. They, too, could provide income. No enemies across the border anymore, no silly walls to be built, and no Hibernian piracy to become a menace. Do note however, that it will be cost- and manpower-intensive for quite some time. Ultimately, when the isles are fully integrated and pacified, they will land you a nice profit. But that's for those who can handle the long haul. In the meantime, you'll have to dedicate resource that you can then not allocate elsewhere. Is that worth it? Perhaps. It would be better than OTL.
As I have repeatedly noted elsewhere, however, I personally think Rome should have refrained from taking Britannia altogether. If that's not on the table, I'd have very much liked to see Hadrian abandoning Britannia - instead of building that damned wall - and allocating the freed-up forces to keep Mesopotamia, instead. Because I don't think Rome at that time could keep both at once (resources were not infinite), and Mesopotamia was simply worth more. Much, much more. (And also, keeping it from the Persians would weaken them forever. If Susiana and Media can be turned into vassal states, too, so much the better.)
