Anytime...
Well, the manufacturers set their sets up differently in the factory and they also give different level controls to different sets. As an example, I have a Mitsubishi 55". The first one I got had problems they couldn't fix. Unfortunately, (for me) I got a brand-spanking new 55" Mits. I say unfortunate because they gave me the next year's model which didn't give me access to the color decoder I wanted (LOTS of red push!). In fact, having access to the color decoder was one of the reasons I'd bought the original set. Now, since then, there have been tweaks put out where I can now access the decoder. So I've been able to fix the red push problem.
So not only do you find different access/settings from different manufacturers, you find different access (sometimes) with the SAME manufacturer! If you're shopping for a set I suggest checking around online and seeing what, exactly, you can do with your set (if you're into tweaking it).
Now, keep in mind, accessing something like the color decoder is, typically, using the service mode. You can REALLY screw things up in your set if you don't know what you're doing. If you're fairly handy/technical, you can find many sites for tweaks. My favorite is
HomeTheaterSPoT. I've been hanging around there since they started and they've got a lot of great info. You can get a lot of info from the general boards but, if you become a paid member, you have access to even more tweak info. The tweaks are pretty-well done with step-by-step directions. Just make sure you record your original settings and take any and all precautions mentioned in the tweaks.
Some of these tweaks are the kinds of things an ISF tech will do. However, as was mentioned, there are many things you probably can't do no matter how technical you are since they require test equipment you probably don't have. This is why there is a market for ISF techs. The extra tweaks (mentioned above) will get you closer to an ISF'd set but not exactly there.
Bascially, I'm a huge fan of ISF calibrations--but they're not for everyone. And, as always, it's your set, you've gotta be happy with it. If you like the way it looks, don't worry about spending the money.
Hope this helps.
The Rickster