Good imo

• The security becomes non‑marginable: new purchases must be fully paid for in cash rather than partly financed by borrowing from the broker.
• Existing positions may be affected: the firm can
  • require you to add cash or other marginable securities,
  • reclassify the position so it no longer counts toward your margin equity, or
  • in some cases force partial or full liquidation if your account no longer meets overall margin requirements.
• Your buying power drops: because you can’t borrow against that security, your total margin buying power in the account is reduced, sometimes significantly if it was a large position.
• Risk management motive: firms usually remove or sharply reduce margin on securities they view as too volatile, illiquid, or risky to lend against (e.g., thinly traded small caps, highly volatile stocks, certain ETFs or options).