Besides the obvious - of getting exactly what you want - custom items can be a better value than mass produced products.

Custom items are better quality than most store-bought furniture, and are at least equal to the quality of high-end items (Ethan Allen, Stickley, etc.).

Costs are often comparable between custom items and equivalent quality mass-produced, store-bought items.

We use solid wood, primarily.  When we use plywood, it is high quality, Made in USA, veneer core.  We never use flake board or particle board.

We use traditional joinery, and rely very little on screws or nails, creating heirloom-quality pieces.

We can make pieces that fit into existing spaces.  Mass-produced items are available only in 'standard sizes.