Yes, they can be placed on just about any plain surface in your garden or balcony area. Some people prefer to support fabric pots with growing trays to provide balance and sometimes help to collect the drains. However, with the soil properly filled into the plant grow bags, you can place them on the ground without any worries.
Also, since grow bags allow you to manage space, they could be placed in one corner of your sunroom or greenhouse without taking much space. Ensure they have access to your water system and sunlight to enable the plant to grow healthy as you try to manage space. Even with poor quality soil, placing the bag on the ground helps the soil to breathe better.