Bitcoin full node - how to run a pruned node, explaining pruning? can you explain please how I can run a "pruned" node instead of storing all 300GB of data? Is there a difference how you turn your btc client into "pruning" mode among the different clients, bitcoin core, bitcoin QT, electrum? 

If i run one of those 3 mentioned btc clients, I would like to know how to turn that program into "pruned mode"? 

Any security factors to keep in mind when using pruned node mode?

Thanks
Running a pruning node simply means enabling the prune setting.

In Bitcoin Core, that can be done either in the bitcoin.conf file by adding a line "prune=N" (where N is a number in megabytes), or through the Qt GUI in the settings screen.

Electrum is not a full node, and never downloads or verifies blocks at all, so there is nothing to prune.

There is no difference in security, only in features. A pruned node cannot serve old blocks to other peers, and can't be used to rescan old wallets (because the block data is not available).