JSF lifecycle - conversion errors clarification.

[A Luis]

In the JSF lifecycle diagram they indicate that there are 2 phases where you can get a conversion error
1) The "Apply Request Values" phase in which the conversion error is
reported back after the validation phase is complete.
2) Right after "Update Model Values" phase in which the local values from the component tree are placed inside the backing beans.

What is the diffrence in what types of conversion errors?
I would of though that if you already properly converted the local values in the
"Apply Request Values" Phase that you wouldn't have to perform yet another conversion in 2) but rather just store them
in the backing beans since there already converted.

Thanks.