Using templates certainly speeds things up and it makes perfect sense to get hold of a template if you don't have the time to generate a plan from scratch. The benefits of using a template are huge because you can have a lot of information you never even thought of already sitting in the template ready to use or customize to suit your particular project.
Another thing to consider when using an internet business plan template is flexibility. The internet is an ever_changing beast and your plan of action will need to change with it. If you choose to follow a template that allows for minimal flexibility then at some point, you will have to choose a different one. The key is choosing templates that already have options built into it. For example, if are using a template to build a mailing list then the key components are getting opt ins and sending emails. The key to getting people on your list is generating traffic to your opt in page. This provides you with a lot of flexibility because there are a hundreds of different ways to generate traffic. If a certain traffic method starts to fail, then you can simply use another one.