Sometimes it helps to think of a prototype as tool for communication – especially when it comes to submitting to EN.
Can the concept be clearly explained without a prototype?
I usually do make a very inexpensive prototype to help illustrate the concept in a video. Some of them are functional, and some are just models.
Also, I learn a lot from making a prototype – it rarely goes without any surprises, and I usually change course a bit in the process.

Thanks Jeff and Scott that help me a bunch! I made a crude prototype- and it came out pretty good! But most of all it worked and it also alolow me to make some changes!

You guys are great!

it depends on what you are doing with the idea. Is it just to submit an idea to a LPS? If so, I probably wouldn’t invest any more than necessary. If you want to do more with the idea, then to prototype it and prove the concept is a must (in my opinion) prior to any other investment. Tp prototype something can mean a lot of different things. What do you want to determine with the prototype is the first question.

I believe doing a prototype of any sort is great and can only help. I don’t think it’s needed though if you can’t afford one, or can’t make one yourself. If your idea is good enough, like the Eggies which was made with just a sketch submission…you should be good. That’s just my opinion. I’m sure others have others.