Creating a model or prototype can help you get the best way to manufacture these devices you've got invented. It may be useful for all sorts of things like figuring out where you should put labels, exactly what the shipping weight will be, the best way to package it, what it cost to fabricate it, and to get feedback from test users. It's really a valuable tool to help you.
If you are going to attempt to raise money to fabricate the brand new product yourself, or if perhaps you're demonstrating it with a potential customer to obtain a big order, you'll need the prototype if you don't curently have a production unit to demonstrate or demonstrate.
People just don't have much imagination. You are an inventor, which means you have an imagination. Before you can invent something you want the idea...plus it takes imagination to generate fun new ideas. Other people, you'll find, accomplish not have the imagination or vision that you just do. Help them out.
With a good prototype or model, your audience does not need to provide an imagination. It makes cool product "real" for them, adding tremendously in your credibility. Having a good prototype can help sell the item even when it isn't even just in production yet.
DON'T delay prototype building until after you file your patent application. You will likely discover flaws or extra features, or discover possible manufacturing problems. With rare exception prototyping is extremely worthwhile. You will find more often than not unexpected discoveries from construction of InventHelp.
Testing is extremely important. A prototype allows you to actually try out your invention inside a meaningful way. You can attempt it with individuals besides yourself if appropriate, and you will then realize that other folks may have constructive criticisms and suggestions that could be very valuable.
By doing a search online you will find model and prototype building companies who can construct it for you unless you have the skills yourself.
Sure there are occasions when a prototype isn't practical, if it's very costly for example, but when it's possible, I highly recommend an invention prototype or model be manufactured.