Synthesizer, Usefull or Useless?

Now a days, Synthesizer was a "thing" that popular used in Modern Music Instumentally. Bands like Linkin Park, Muse and Indonesian Famous Band DEWA19 use this hardware. So, What is Synthesizer?

A synthesizer is an electronic instrument that utilizes multiple sound generators to create complex waveforms that can be combined into countless sonic variations through various waveform synthesis techniques.
"Synths" generate sounds and percussion sets by utilizing a number of different technologies or programmed algorithms, each with their own strengths and weaknesses. Among the most popular waveform synthesis techniques are subtractive synthesis, additive synthesis, granular synthesis, wavetable synthesis, frequency modulation synthesis, phase distortion synthesis, physical modeling synthesis, sample-based synthesis and subharmonic synthesis.
Synthesizers are often controlled with a piano-style keyboard, leading such instruments to be referred to simply as "keyboards". Several other forms of controller have been devised to resemble violins, guitars and wind-instruments: there are also several automatic means of electronic control.

The first electric synthesizer was invented in 1876 by Elisha Gray, who is best known for his development of a telephone prototype. The Hammond Novachord was an early but unsuccessful harbinger of synth technology in the 1930s-40s. Robert Moog introduced the first commercially-available modern synthesizer in the 1960s. In the 1970s the development of miniaturized solid-state components allowed synthesizers to become self-contained, portable instruments. By the early 1980s companies were selling compact, modestly-priced synthesizers to the public. This, along with the development of Musical Instrument Digital Interface (MIDI), made it easier to integrate and synchronize synthesizers and other electronic instruments for use in musical composition. In the 1990s synthesizers began to appear as computer software.

 There's any type in Synthesizer?
Additive synthesis builds sounds by adding harmonically related waveforms. An early analog example of an additive synthesizer is the Hammond organ. Additive synthesis is also the principle of Wavetable synthesis, which is used to implement real-time synthesis with minimum hardware, commonly used in low-end MIDI instruments such as educational keyboards, and low-end sound cards.
Subtractive synthesis is based on filtering harmonically rich waveforms. Due to its simplicity, it is the basis of early synthesizers such as the Moog synthesizer. Subtractive synthesizers use a simple acoustic model that assumes an instrument can be approximated by a simple signal generator (producing sawtooth waves, square waves, etc.) followed by a filter. The combination of simple modulation routings (such as pulse width modulation and oscillator sync), along with the physically unrealistic lowpass filters, is responsible for the "classic synthesizer" sound commonly associated with "analog synthesis" and often mistakenly used when referring to software synthesizers using subtractive synthesis.
FM synthesis is a process that usually involves the use of at least two signal generators (commonly referred to as "operators") to create and modify a voice. Often, this is done through the analog or digital generation of a signal that modulates the tonal and amplitude characteristics of a base carrier signal. More sophisticated FM synths can use up to 4 or 6 operators per voice and also often use filters and variable amplifier types to alter the signal's characteristics into a sonic voice that either roughly imitates acoustic instruments or creates sounds that are totally unique.
Phase distortion synthesis is a method implemented on Casio CZ synthesizers.
Granular synthesis is a type of synthesis based on manipulating very small sample slices.
Physical modeling synthesis is the synthesis of sound by using a set of equations and algorithms to simulate a real instrument, or some other physical source of sound. This involves taking up models of components of musical objects and creating systems which define action, filters, envelopes and other parameters over time. The definition of such instruments is virtually limitless, as one can combine any given models available with any amount of sources of modulation in terms of pitch, frequency and contour. For example, the model of a violin with characteristics of a pedal steel guitar and perhaps the action of piano hammer. When an initial set of parameters is run through the physical simulation, the simulated sound is generated. Although physical modeling was not a new concept in acoustics and synthesis, it wasn't until the development of the Karplus-Strong algorithm and the increase in DSP power in the late 1980s that commercial implementations became feasible. Physical modeling on computers gets better and faster with higher processing.
Sample-based synthesis One of the easiest synthesis systems is to record a real instrument as a digitized waveform, and then play back its recordings at different speeds to produce different tones. This is the technique used in "sampling". Most samplers designate a part of the sample for each component of the ADSR envelope, and then repeat that section while changing the volume for that segment of the envelope. This lets the sampler have a persuasively different envelope using the same note.