I don’t think it’s safe to reuse freezer bags when they’ve been used to store meat or dairy but I do use them to hold smaller bags filled with practical-sized portions. The smaller bags don’t need to be freezer friendly since the larger bag will act as backup protection for my food.
I also reuse the larger freezer bags to hold paintbrushes for projects that I’m not finished with. I just place the brush in the bag, seal it and stick it in the freezer. The next day I can continue with my project and didn’t have to wash the brush twice.