Do random plants growing on temporarily unused soil deplete it or enrich it?

I have a couple of planters i’ve dumped a mixture of soil and compost that i’ve yet to plant ( waiting for the seedling to germinate). In the meantime plenty of cucumbers , tomatoes and other random things are beginning to germinate there (from all of the kitchen scrap seeds I supposed) and I wonder if I should let them grow until my seedlings mature (and then kill them) or kill them now.