As mentioned above, wood panel is already hard and rigid, and can be easily transported while layers are wet and still drying. A rigid surface is best for sanding and pouring techniques.
It can cost less then stretched canvas. Canvas stretcher bars are made for reuse and are costly. A local carpenter or wood worker can make several wood panels at a time, with cost savings to the artist. Carpenters will generally charge per hour plus cost of materials, while purchasing stretcher bars and canvas have extra added retailer costs that are put on the final price.
Wood panels can be made with different woods and braced to minimize warping.
They are more sturdy then canvas. This means they will last longer than canvas given similar environmental circumstances.
If you want to paint over an old painting on wood panel, it is easily remedied by sanding off any old texture and paint. I don’t recommend repainting over old paintings on canvas. It is difficult to properly sand the texture off, and isn’t as strong as wood panel for the added weight when applying extra layers.
Confused about masonite, hardboard, and how to choose the right wood for panels?
These can get heavy when working on large size panels.
CANVAS ON WOOD PANEL
You can also combine the two. Paint on canvas, then adhere the canvas onto wood panel.