It depends what you want to defend against but large plates might be good against claws - which are designed to cut through flesh - but there are some aninmals with the jaw strength to break bones.
But yes, bone is harder than flesh and would offer more resistance, therefore it is a form of armour.
Thicker bones give more protection but also add more weight. If we aren't changing the human too much (ie having a, literal, exoskeleton and no internal skeleton) we can look at how much weight is being added.
I found something that quotes human bone density as $1600$kgm$^{-3}$. Another source says the surface area of a human is $1.5-2.0$m$^2$. So, for a thickness of $1$cm of bone (can make this thicker or thinner if you like, this is just a ball park).
We get: $$1600 \times 2 \times 0.01 = 24 kg$$
This is quite a large proportion given average human body weight is around 80kg (I couldn't put that link in but a quick google shows it). You can tweak those numbers if you like. Maybe you only have plates on 1 square meter but you're still left with 12kg extra mass.
Humans are designed for running long distances, running away from predators or, as a pack, towards prey. 279
The extra mass would seriously inhibit this and mean your new humans need to become bulky fighters rather than runners.
Some edits:
Firstly a few people pointed out that, in the army and such, modern humans can train to run with heavy armour (see <PERSON>'s comments). I completely agree we can manage, however with the OP asking about predators I had (perhaps incorrectly) assumed this meant they were living in a hunter/gatherer type society where any and every edge you could get was essential. It seems to me humans evolved to run long distances and, assuming this was for survival, the extra carry mass of the bone would render this survival tool less efficient. This is why I proposed they would become bulkier fighters compared to their unarmoured counter-parts.
Secondly dlatikay provided this source which provides figures for the density of different bone types. They said:
So the weight could range from ~23kg (solid-massive) to ~6kg (spongy).
Which provides us with different uses for the bone - perhaps even different types (or classes) of armoured humans. Ranging from those with thick solid armour who might risk a run in with a heavy clawed animal to the lighter, spongy armoured humans who may be more useful as scouts, mountain climbers who may be better equipped to take a fall or some other attack where the force is spread out (rather than in a sharp tooth or claw). 162