Tumble drying will make your towel look and feel fluffier than drying your towel on the line. If you're line-drying your towels, give them a good shake out before folding. This helps prevent the fibres on your towels "setting" and becoming hard. No matter how you dry your towels, remember that using fabric conditioner will make your towels harder over time, not softer. So stay away from fabric conditioner and you'll be snuggling up in soft towels for much longer.
Tumble drying your towel is a lovely way to open up the cotton fibres so they're wonderfully soft and absorbent.