Lite nodes can't sync or mint blocks, and they also have a very limited ability to verify unconfirmed transactions due to a lack of contextual information (i.e. the blockchain). For now, most validation is skipped and they simply act as relays to help get transactions around the network. Full and topOnly nodes will disregard any invalid transactions upon receipt as usual, and since the lite nodes aren't signing any blocks, there is little risk to the reduced validation, other than the experience of the lite node itself. This can be tightened up considerably as the lite nodes become more powerful, but the current approach works as a PoC.
