The one thing that is almost useless for a writer is the high-level account of kings and wars. But it has one use that probably can't be easily replicated by anything else, though it is not directly useful in writing.
It provides a mental framework for what happens before and what after, so you can mentally file your research in the proper era and avoiding confusing things too much. Things change from era to era. It's not safe to file them all under their locations, or even their era if you're not precise enough.
Like "Ancient Greece." Homer is Ancient Greece, and so is Aristotle. But one is Heroic Age, and the other Classical Era. This explains why in Homeric Greece, you have to swear to your truthfulness by the name of a god, to add blasphemy to your sins if you lie -- the gods are offended by having their names blasphemied against, but are not worked up against lies -- but Aristotle can cheerfully cite as an example of rhetoric a priestess who warned her son against politics, because, if you tell the truth, men hate you, and if you tell lies, the gods hate you. Similarly Odysseus has a hard time getting back because he has ticked off Poseidon, and Menelaus was stranded in Egypt until he forced Proteus to reveal which god he had to sacrifice to, but all the others, regardless of what crimes they had committed, made it home swiftly and safely. In a trial recorded in classical Athens, a man defending himself against murder pointed out he had taken a sea voyage and not been shipwrecked -- surely the gods would not have tolerated such a thing if he were a murderer. (The worst confusion I saw about this was on the History Channel where the voice over solemnly cited Herodatus as an ancient writer -- about the building of the pyramids. He's closer in time to us than to the pyramids.)
The Middle Ages get a lot of grief about this. Not helped by the Romantics who seized on them as the archetype and model of their views, any more than the Ancient Greece was helped by the Enlightenment treating it as the archetype and model of their views. But even getting past that, there is a lot of lumping. Masquerade balls were not a normal product of the Dark Ages. Indeed, knighting a knight did not start until the Dark Ages were fighting. That is why the medieval Latin for knight is miles -- soldier. It was when the Third Estate did not consist solely of drudging peasants but included wealthy merchants, who had clout, that the military class decided it needed to separate itself with the ceremony. (Dumb and self-defeating. Once you make it a ceremony rather than fighting, a merchant incapable of holding his own in a fight can weasel his way into your class by going through the ceremony.) Or tourneys. The original ones were just the melee -- a brutal fight, which the Church tried to ban by forbidding burial rites to any man killed in one, as they often were. Then they added jousting. It was a long time before it reduced to the jousting, and we got the pageantry that Elizabethean jousts were, more than actual fights. A progress toward the courtly entertainments of the ancien regime.
Then there are those who project the ancien regime back into medieval France. Between the power of the king, and the feudal duties -- some lords were fond of digging up any records at all of any feudal duty and demanding that it be paid unless the peasants could prove it had been foregone, meaning that peasants during that era had to pay several when in real medieval times, they generally had one at a time, because one duty was given up for another, in a verbal agreement.
Or keeping track of China through the dynasties -- and lack thereof. There's a certain problem in that Chinese history tended to be molded to the theory of the mandate of Heaven, which can make it hard to work out the ends of dynasties -- the last emperors being not so evil, and the transition not so clean as the theory called for -- but a lot of info is nevertheless there. And one can trace the process by which the practice of perpetual commerating emperors other than the dynasty founder came into play, or the way that tax burdens in certain eras crushed out the small farmer.
And in Japan, there were the different eras, like the Heian -- where the emperor was young, often a child, and married off an older wife by the noble family that was controling him at the moment, but could on occasion act against them -- vs the Shogunate, where Francis Xavier described the Japanese as having a Pope and an Emperor -- those being the Emperor and the Shogun. Which, if anything, overstates the political power the Emperor had at the time, because the actual Pope had more clout.