Standard color profiles are kind of like units on a blueprint. RGB images store an integer value for each of the red, green, and blue channels. These values don't really mean anything without some kind of reference.

If I told you I have a box that is 8 x 8.5 x 40, you can construct a relative concept of the boxes shape, but without units, you don't know if it's small enough to hold in your hands or the size of a shipping container.

Color standards work in a similar way, by mapping those relative values into a visual gamut. sRGB is one range of color, AdobeRGB1998 is another, but both can be represented in the same raw values.

Monitor and printer profiles serve a different purpose. To extend the metaphor a monitor or printer's color reproduction is more like building something with a piece of string as your ruler. It's about the right length, but it's not perfect. It also changes over time as the components age, like a string stretching over time, or contracting when it gets wet.

A monitor profile is designed to compensate for these variables. The diagram says 1 meter, and I have a string that is supposed to be a meter long. It will be close. But if I measure the string and discover it's actually 101cm long, I need to adjust my measurements accordingly or my box is too big.

Profiles are bound to the file, not the software. The default profile is just a preference that will be used for all new files, files that do not contain a profile, and to display a warning if you open a file that isn't in the same color space as your workflow.

If your hypothetical pixel value is <30,40,50> in sRGB, it only has a true meaning because it's in sRGB because sRGB is a map from a pixel value to an exactly color. sRGB then works as a standard unit of measure throughout the process. In a camera, it is used to encode the real analog signal from a sensor to an accurate pixel value.

When it sends it to the video card, the instruction is not "display <30,40,50>" which is a code with no absolute value (it will just assume something). Instead it says "display <30,40,50> in sRGB" which is a very precise measurement. Then the graphics card looks at its monitor profile and says "they want <30,40,50> sRGB, but the monitor won't display the right color if I send it <30,40,50>, to get the right color, the profiles says to send <31,39,52>".

You never want to use a monitor or printer profile as the profile in the image itself. Then entire system works because, no matter what standard profile you use, you have a solid point of reference. To continue our analogy. It would be much easier to build a box with the length 7.6cm than a box the length of a pencil that has been sharpened, had 400 words written, sharpened again, wrote 100 more words, then the lead broke, sharpened again, and drew 3 flowers and a duck.

With a standard, every element of the process can be calibrated to the same reference without ever having to know what and how many other elements are in the process.