Why Just Round Shapes?
Lathes turn a piece of wood - around a single axis. Two centers define the centerline axis. Circles cut around that centerline creating a three dimensional object. Slice it anywhere - square to its centerline - and you have a circular cross section on each side of the slice.
When you apply a cutting tool to the spinning piece of wood it removes some. After a while it starts removing wood - ALL THE WAY AROUND the spinning wood. The process automatically creates "round shapes".
You can make different sized round shapes - a cove, a bead, an ogee, a groove - and combine them to create pleasing forms - which are round in cross section - AND symetric - at least symetric about the piece's axis of rotation.
You can hollow your "round" turning - or pierce it - or color it - or texture it - or patina it - but you're still stuck with ROUND.
But who says you HAVE to keep turning 'til you reach round? What if, as you're Roughing To Round, you stopped - maybe once you've got a quarter of the blank's cross section cut - just part of ROUND - an arc?
Who say you have to turn THE WHOLE piece using just ONE pair of centers? What if you turn part of the blank to round - one one centerline - then remount the piece between two other center pairs (centers come in pairs - one on each end)