Adding PHP to HTML Code

[eluser]BigJoe[/eluser]
I was told and from what I can see in the video tutorials that CI all so requires php code to be added in the HTML Pages. I was and have been told that this is not a good idea to code in this way. If every one is telling me not to do this. Then why do all the video tutorials I have seen and what I been reading say it's Ok to do this. I have been told that it makes it easy for hackers to hack web sites by doing this. and there or maybe other reasons too.

Please post views and options.

Joe