Rscript + PHP exec() command vs rapache

Say I want to have a simple web app that takes some user input, performs a quick calculation in some predefined R script, and returns some cool looking graphic with say ggplot. One way to do this would be:

1. Have PHP accept some input from a web form
2. Sanitize the user input in PHP
3. Send the arguments to some pre-written R script using some combination of the PHP exec() command and Rscript
4. R does some calculations and saves the plot graphic to the server as well as some meta info to a MySQL database
5. The client can then access their cool new graphic from their web browser

This seems fairly straight forward to me. Thus my question is, what advantages would the rapache package have over the process described?

First off, rapache is not a package. It's an apache module and a set of conventions, really a system, for creating web applications written in R...

The advantage is speed. The disadvantage is you'd have to write a bunch of R code. Some might disagree with me on that one, though.