'Pruning' allows node operators to save 2/3 of storage space while keeping the full transaction history. Pruning works by removing 7/8 of unnecessary ring signature data. The 1/8 remaining data will be available to the other nodes and will be used to sync with the network. Other pruned nodes will have a random 1/8 of the data, which they will also make available to the network. There are no privacy or security downsides when using a pruned node.
There are three ways to prune:
Pruned nodes are very useful and preferable to remote nodes, but if possible, users should run a full node and opt for pruning only in case if necessary.