All routers within an OSPF area keep a link state database (note that this is completely separate from the main routing table), where they're aware of all other routers and their links within the area. Each router within the area builds a topology tree of the area, with shortest paths to all other links/routers with itself as the root. This last part is important.
When an area grows large, the link state database (the tree or topology) that each router must maintain also grows large. This means that it can become more and more intensive for the router to process link state (topology) changes as there are now a large number of entries in the link state database. The tree grows larger and is more difficult to "keep up" with as there become more and more branches/leaves of the tree. Something else to keep in mind is that as the area (network) grows larger, there is greater potential for link state changes, and thus a greater potential for recalculations of the link state database. While the details of which are somewhat "out of scope" of this answer, the OSPF link state update process is also relevant here.
Ultimately, as a single area grows larger and larger, the SPF recalculations themselves will take longer to complete, and you have more risk of those SPF recalculations happening due to various reasons - the moral of the story is your routers' CPUs will be sad.
The "advantage" of OSPF areas is that they provide a means to alleviate the demands placed on the routers if they were otherwise in a single area, by way of cutting down entries within the link state database and pushing responsibilities of the link state database maintenance to area border routers for their respective areas. It allows for a way to keep the tree size manageable.
Thorough thought and planning is mandatory for designing/implementing multi-area OSPF - there are a number of situations where poor design in multi-area OSPF can bite someone.
Using areas doesn't necessarily increase the "speed of communication" but it can have significant performance benefits (if done properly) to the routers in your OSPF network, especially if your network is very large, because their CPU's aren't having to work as hard.