Capacitors can be used for many purposes - for debounce of inputs, power isolation, curcuit loading. Some microcontrollers have D/A converters, oscillators, or transmitters built in and require external capacitors to operate these at specific frequencies.
Because that's what Intel specs as required in order to ensure proper operation.
c1 and c2 capacitors with crystal eliminates the Harmonics(Unwanted frequencies) .
The main intension is to eleminate high noice frequency which was jenarated by crystal. Regards, Narayana Reddy