[mslot]

One caveat to keep in mind when using the binary format is that arrays of custom types are not portable across databases because the serialized array contains the OID of the custom type, which may be different on the other end.

The other thing to keep in mind is that text or CSV can be much more compact for data sets with many small integers or NULLs. On the other hand, the binary format is much more compact for timestamps and floating point numbers. In general, binary format has lower parsing overhead.