There is widespread consensus that it is worth optimizing the way IP is mapped onto Lowpans.
Because of DeviceConstraints, many Lowpans will be energy-limited (e.g., battery-operated, with a battery lifetime requirement of a couple of years or more) and need to limit the number of messages that nodes are processing to an order of a couple per hour or even per day. This calls for a need to minimize background traffic (NeighborDiscovery, routing, discovery).
The limited MTU of Lowpan's underlying 802.15.4 calls for some restraint in message sizes. While 802.15.4 messages can be concatenated to form Lowpan messages, this causes additional overhead. The 802.15.4 MTU is 128 bytes, up to about 47 of which can be taken by MAC overhead, security etc. This calls for some form of header compression, as the IPv6 header alone would consume half of the rest.
It is not quite clear what we are optimizing for. Three groups of applications (which are rather heterogeneous in themselves) have been identified: