Combat triggers encourage aggressive play and reward you for connecting with attacks
It will not stop you from playing these cards even if you have no Benched Pokmon to replace them, so playing them while you have no Benched Pokmon will cause you to immediately lose by having no available Pokmon
When creating a deck there are a few different ways that players can go about designing it
"This is a popular, flexible mechanic with fun gameplay
There are cards to quickly fill your graveyard, such as Stitcher's Supplier and Faithless Looting , and then plenty of cards that bring milled cards back to either your hand ( Graveshifter , Eternal Witness ) or even directly into play ( Deadbridge Chant , Liliana, Death's Majesty )
That's the best offer I've seen, so it's unlikely to last long