yep! They get turncoats that are basically dead cards. They then have 2 choices: keep them in hand, but that means they have less acces to useless cards. Or discard them, powering up the confeatheration and letting them score more.
And yeah the dominant strategy (probably) is to focus your infiltration on one opponent. Specifically one that values cards a lot. That gives you the highest chance of them actually discarding cards.
Players of course can discard them when they have 6+ cards end of turn. But they can also discard a card on their turn to draw a new card, this is needed especially for eyrie, but factions like moles and lizards also value cards that actually have suits.
Intended is that after you draw, its no longer your turn so you cant discard turncoats that same turn to draw a card.