Placeholders compensate for missing or incorrect investing transactions by forcing Quicken’s share balance for a security to match a specified value. This is usually the share count downloaded from your financial institution (FI).
Because transactions are missing or incorrect, Quicken will not be able to compute the cost basis or performance for the affected securities.
Placeholders also prevent new transactions like Bought and Sold prior to the Placeholder date from affecting the account’s cash balance. This shows up as N/A in the Cash Amt column of the transaction list.
You can go back and resolve the Placeholders later on if you want. For information on resolving placeholders, please see this FAQ:
https://community.quicken.com/discussion/7267839/quicken-faq-managing-placeholder-entries-in-quicken-for-windows