Difference between low level and high level modulation

Can anybody please tell me the difference between low level and high level modulation? Also could you provide me with specific examples and advantages and disadvantages of each?

Low level modulation is modulating an RF source at a power level of mWs. This has to be increased to the transmission level power by amplifiers, which may have to linear depending on the form of modulation.
High level modulation is when amplitude modulation is applied to a RF power amplifier, so the modulator has to supply half of the carrier power.
Frank

In low level modulation, modulation takes place prior to the output element of the final stage of the transmitter. For low level AM modulator class A amplifier is used.
In high level modulators, the modulation takes place in the final element of the final stage where the carrier signal is at its maximum amplitude. For high level modulator class C amplifier is used.
An advantage of low level modulation is that less modulating signal power is required to achieve a high percentage of modulation.

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http://www.utem.edu.my/myweb/fakrulr...20part%202.pdf

These two methods were done in the vacuum tube past for amplitude modulation. It was an economic tradeoff. The low level method saved on the cost of the high power modulator and transformer in exchange for the lower efficiency of a linear amplifier.