I am Not a Third Party.

Here are some reasons you might want to use one.
 
For thousand of years, philosopher/planners have long debated whether they plan large events themselves or hire an “expert” to help.
 
You may not have known this, but during the first Olympics it was decided to save some drachma and the whole shebang was assigned to an EA. Not that they weren’t supremely qualified in their job… but this was something they knew nothing about (although they may have thought they did). “What could be so hard”, they said. “Just hire a caterer (everyone loves lamb), a band (can we get Orpheus?), invite everyone on the list, big guys will wrestle, and we’ll have a party. I love parties”.
 
Well, as it turned out, the Athenians were seated next to the Spartans (AWWWKward!!!), the Discus-Throwers sign had to be hand-chiseled at the last minute (talk about overtime – and if you think unions are tough, try dealing with the stone-cutters guild on a weekend), Aphrodite’s welcome amenity was WAY nicer than both Athena’s and Hera’s (Google “Trojan War”), and when Hades’ VIP chariot didn’t show up, all Hell broke loose (literally).
 
Yes. I’m a riot. :)

The bottom line question: Is the mark-up you pay to an Event Management Company more or less than what you will have to pay when things don’t go the way you expected?

I am not a full-service Third Party. I am The Guy Who Introduces Good People to Other Good People (ask me for referrals any time)… but I have spent many years of my career as a third-party guy and have been on all sides of the table in this discussion. Here’s my take on it (in a few paragraphs) for The Basic Scenarios…

You have to plan a small internal meeting...

in a destination you are familiar with. You know who is coming, need some rooms, a place to meet, some F&B, and an off-property activity. My advice: Do it yourself. If you like details, everything will be fine. (Important Note –read the hotel contract before you sign it and don’t hire any vendors no one in your professional network has ever used. Did I mention I was a free referral service?). 

Next level… it’s a bigger meeting...

you’ve done this before but you have a lot on your plate, there are several simultaneous tracks, all of your Executives will be there and you can only hold a few hands at a time. Consider one of the zillion “independent” planners or smaller “houses” out there, some more competent than others (ask me and I will make some recommendations), who will work on a contract/fee basis. Give them specific pieces of the project they are accountable for. They can relieve some of the burden, advise you on some of the tricks of the trade (they will read and actually understand the hotel contract), and be in places where you can’t be because you are someplace else. When the meeting is over, they move on. It’s worth it.

One step up… You have to organize a large conference...

top customers, users, developers, investors, the press… and your executives will be there too. The whole world is watching. We are not just talking about meeting logistics. It’s a Branding Thing.  You’ve got to think strategically and identify your audience, avoid conflicting industry events, formulate a message that will inspire your audience to attend, design logos, manage sponsors and exhibitors, etc. times a million. Never forget that the logistics of the event reflect your brand, so all of your vendors better be up to snuff, because your audience (and your boss) will not blame the AV guy if the lights go out. And so on.

What can a good third-party do for you?

If they are good (that’s a big question), tell them everything you need to do, everything you want to do, and how much you have to spend (and be honest)… and if they are good (still a big question), they will come back to you with questions and then options...lots of them. The good ones not only know what they know, they know everyone who knows what they don’t know (just as important), and they walk you through the insane process of it all. Their job is to make you look good. The good ones want your repeat business.

Sure they mark it up (remember to keep your eye on that… has to be transparent). Think of them as an insurance policy… they are paid not only to make sure things go right, they are paid to think of everything that could go wrong, prevent it from happening, and have a back-up plan when it happens anyway.