Emulation gives you a chance to play games you might never get to play.
Or allow you to relive your youth.
You don't have to store the equipment and scour for parts in garage sales hoping you're not getting ripped off or paying 5 bucks for something that's worth 50 cents.
Emulation takes out half the fun of going to swap meets and such. But the down side of this is people paying outrageous amounts on auction sites like e-bay for "garbage" because they're collector items. Listen people, Atari games aren't worth a lot of money. Sort of like 8-tracks there's very few Atari games that are worth over 10 bucks used (of course some say that some games weren't worth 10 bucks when they were new.)
However, most of the companies that made the games either don't exist anymore or don't consider it worth the time or money to hassle people. And there are other legal questions involved that pass over my head.
Now here's the argument that most people have debated for the last few years. Does playing a game on an emulator constitute a real experience? This is a similar argument about playing a Atari ( or any other console) version of an arcade game. But to me, playing an emulated game is just like watching a movie on tape or DVD instead of seeing it in the movie theater.
It's a mixed bag control wise. Some games you can use the mouse for the paddle but unless you have one that lets you use the space bar and arrow keys be prepared for finger cramps.
Another Pro of using emulation is that graphically Atari games look just as good on a computer screen as they would on a TV. The same goes for sound.
Now a big Con is that some older emulators will run the games faster then they originally played. Playing at such a fast speed makes the games hard to play. Luckily, most Windows emulators have worked out the problem of running the games too fast.
Also not all ROMs and emulators work together correctly. That's the problem with 5200 and the 7800 emulators I've tried. Some of the games never get past the Atari logo screen or some of the controls needed to be tweaked and such.
Another piece of advice is stick to emulators that are at least Windows 95 compatible. That way you don't have to use clunky DOS commands for resetting options and such. You can get a front-end for the DOS emulators, but its just easier to get the Windows version instead.
Also one last note: When you go to a emulator site like classicgaming.coms vault, and they have the emulator author's web site listed, I advise going to the website regularly. That way you have the latest version since some sites don't update as quickly or as frequently as the actual author.
When it comes to emulators, I suggest you try many different ones until you find the one that is best for you.