Well personally I think that the biggest advantage if having a tax id is that most of the REAL Wholesalers and businesses require one. And with the legit businesses that do require on you normally get better prices and service to boot..
Also, by having a tax id, it allows me to take certain tax deductions that I normally would not get..and every little bit helps when filing taxes each year..In addition to that, so businesses look at you having a tax id as showing that you are really a business person and not just a 'tire kicker' or some one who is just going to buy once and be gone...
In most states the cost of on is 20 bucks or less and it only takes a few minutes to fill out the application, so it's not really a big deal...