If you want to draw 5 cards a turn, you have to discard at least 3 cards to redraw to that many.
With making 1 worker a turn, that means you can play 1 other card and keep drawing 5 cards each turn.
Given that playing two 1 cost cards gives you more stats/abilities then playing one 2 cost card, you can see that a “card” effectively is part of the cost of playing something (this can also been seen in how much it costs to draw 1 card).
Ignoring a lot more factors (such as smaller deck size, etc) which just increase the value of playing cards, we can therefore estimate that a card has a value of around 1.5 gold (this may vary due to colour/circumstance etc but is a good estimate)
So by discarding 4 instead of 3 you could argue that you are throwing away 1.5 golds worth of value, which should suggest that before you do it, there should be a good reason into why you are not playing that card.
EDIT: @Azuset as an example, say you play a Nautical Dog on T1 with zane. This means that if the following turns are the same, that the dog could trade with the Tiger, meaning that zane lives to turn 3 and calamandra is on a lvl 1 hero. As you can see, the small difference on T1 can have very large impacts further down the road (which is this case the board difference would be far greater than 1.5 gold would suggest).