When I overwrite a file while uploading via SharePoint CSOM, does the identical version consume space in my personal OneDrive for Business?
Yes it does, but not to the degree at which versioning in SharePoint behaved in the past. Previously it would take copies of the file leading to massive space consumption if you didn't put limits on version retention, you could fill up your quota fast.
Shredded Storage comes in two parts: part one is about getting the document to the Microsoft SQL Server and part two is about storing it in SQL. Part one is an enhancement of the Cobalt feature introduced in SharePoint 2010 and part two is a new feature introduced to store deltas of documents in SQL.
The shredded storage componet is storing delta changes, leading to much smaller consumption. If you look at your OneDrive for Business site, the default nature is to keep 500 verions. If that were on prem in 2010, you'd blow through your allocated space in a heart beat. In 2013 it isn't a problem.