The value binding is basically used at the add/edit change event.
<div>
<label>Description</label>
<textarea id="txtDescription" onkeyup="return checkAbbreviationKey(event)" data-bind="value: Description, valueUpdate: 'afterkeydown'"> </textarea>
</div>
<div>
<label>Description</label>
<textarea id="txtDescription" onkeyup="return checkAbbreviationKey(event)" data-bind="value: Description, valueUpdate: 'afterkeydown'"> </textarea>
</div>