The perfect potting mix for an indoor plant is one that mimics the plant’s natural substrate as closely as possible to form a desired balance of moisture, nutrition and aeration.
For some plants that grow in arid environments this requires forming a free draining, nutrient poor substrate.
For others naturally found in a tropical ecosystems a nutrient rich, moisture retaining substrate is essential.
Whilst for air plants, who draw moisture and nutrients straight from the air, no substrate is needed at all.
The health of your plants starts from the ground up so having an appreciation of what soils your collection would benefit from is key.