Generally you only need an EiN if you have employees, have a keogh plan or are a corporation. As far as I know, you can obtain an EIN even if you don't need it. As Randy said, I doubt that it would ever be an issue at any reputable agency ( and that, of course , is all of them

)
The only other point I would make is that in my opinion, when it comes to the IRS, the best strategy is to blend into the woodwork and not draw attention to yourself, which an EIN might do if you don't require it. Just my paranoid side coming out.