The form is saved as jobs/booknest-freestyle/config.xml in JENKINS_HOME, the script inside a <hudson.tasks.Shell> element, and that XML is the only copy of the job. For one small job that is fine; for a team it breaks down:
No review, no history. A change is a click on Save, with no pull request, diff or blame.
Build and code drift apart. A new test dependency needs a code change and a job change.
One job per branch. A feature branch means copying the job, and later deleting the copy.
Workflows become job chains linked by triggers, with the whole flow visible nowhere.
No durability. A freestyle build running during a controller restart is lost; Pipeline resumes (Restart Mid-Build).
Hidden state and clicks. The workspace carries over (Freestyle Jobs), and this five-part job's configure page is about 3,700 pixels tall. Fifty repositories mean fifty forms kept consistent by hand.