Decorating intimate gatherings at home is vastly different from decorating a formal 300+ person wedding at a hall.  You need more materials, larger storage space, a larger budget, and to top it off you don't have a month to leisurely decorate.  On the contrary, you usually have a 2-3 hour window at a hall to setup.  Talk about pressure!

In this day and age of Do-It-Yourself (DIY) and all the multitude of resources available to find the perfect decorative elements, many opt to forego Professional Decorator services.  And if you have a huge budget to buy everything (buying items is usually at least 2 times more expensive than decorator's prices), a huge storage to store everything before and after the event, and a huge cavalry of family and friends that will be there day after day for a month to go to a multitude of appointments all over the state, work with all the separate vendors, pickup, prep, transport, setup, cleanup items (essentially 3 times- when picking up items from all the different vendors, the day of, and the colossal chore of cleaning up and reorganizing items to store), AND still be able to spend time with you, have time to get themselves ready, and still have energy to ENJOY the events - then POWER (and props) TO YOU!!!

In addition, there's a lot of insight that decorators have that can help avoid little mishaps the day of.  The worst thing is to run everyone to the ground prepping only run into unavoidable issues the day of - issues that a professional would have circumvented and/or be able to work around the day of.

So for those of us that aren't superhuman and don't have superhuman friends/family at our beck and call, it's strongly encouraged to hire professionals.  If you're the type that needs to keep control - find a decorator that will work closely with you step by step.  And if they don't have items that you want, have them get them.  But leave the work to them!  In the end you'll save money, time, energy, tiffs with those that you love, everyone will have fun at your event, and your big day will look EXACTLY as you imagined!