Imagine - You decide to buy a new mp3 player online. You do a search in Google, and you are shown a bunch of web pages. You click on the first link, and are taken to a very nice website that sells mp3 players. You browse around for a while, and find the model you want. You need the item shipped right away because it is a Christmas present. You need to know if it is in stock and will it ship right away. You need it in a few days. You don't see anywhere on the site that tells you when it will ship or how long it will take to be delivered to you.
You now have a two options, send them an email and hope they respond in a timely manner, or head to another website to look for one with priority shipping. Because you need to know now, you head to another website. Consider what would happen if the site you were on had a live help option. You would click the live help, and ask to see if the item is in stock and if it can ship tomorrow. The website owner can answer you immediately and you are happy.
You pull out your credit card and you have your mp3 player paid for and on it's way. Customers love instant gratification. They love to find answers right away. They don't have time to spend trying to decide if your website is a good place to buy. Let me sum it up. Don't give your customer any reason to leave your website. Give them what they want immediately and you will be improving your chances of making the sale. And you will give your customer as sense of trust so they will likely come back to you and buy again.