In short, it is most preferable to plant sparsely and over-light singular plants than planting many and having no guarantee of anything growing at a steady pace.
Herbs, flowers and other simple non-fruiting plants can be planted densely and still be quite easy to light adequately. Anything from small bean plants is already creating constant shadowing and over-growing issues that require extremely sparse planting to be avoided. It is understandably tempting to plant a ton of small-looking plants such as radish and turnip that remain quite small for a long time. Ultimately, they those plants will become a major and a recurring problem later down the line.
The compromise with planting “big” plants yet wanting to not “waste” the space between the sprouts, is to plant small flowers and herbs in the space between them. E.g. chives and dill are very unlikely to cause any shadowing issues. You can also consume those herbs and use them as spices if they somehow manage to overgrow, making the situation a win-win in any case.
Ransacked Crash Site 