An offer without deposit does not have the holding deposit pre-authorised. If your offer is accepted, you must put down a holding deposit manually and as soon as possible. It will not be automated.
This increases the risk of losing the property as, until the holding deposit is paid, the listing will remain on the market and open to other renters. Owners don't prefer offers without deposits because it gives them less of a guarantee of your financial commitment.
Example: You've made an offer without deposit on 7 Thalia House E14 9RU and it has been accepted. You are given 24 hours to pay the holding deposit and decide to pay it in a couple of hours when you are free. During this time, 7 Thalia House E14 9RU stays on the market.
Another tenant makes an offer with deposit which also gets accepted. Upon acceptance, the holding deposit is paid immediately and automatically. They have secured the home. While your offer was accepted first, the property is still fair game to other renters until you submit a holding deposit.