If you never sign in, none of your data ever reaches Abledo's servers — see "Frequently asked questions". Once you sign in, the full detail of what's stored is in the Privacy Policy, linked from this page's footer.
Deleting your account
Settings → Account → Delete account removes your account and everything tied to it: your tasks, projects, notes links, progress, billing record and reminder subscriptions. If you own a team, ownership passes to another member automatically, or the team is deleted if you're the only one left in it.
This can't be undone. If you'd rather just stop syncing, signing out and continuing without an account is reversible; deleting the account is not.