What's the reasoning behind changing pilot tones in OFDM?
Advantage of pilot pseudo-random sequences in standards (with examples are taken from LTE) :


Interference from other sources with different identities (UE ID, Cell ID, ...) are mitigated if detection by correlation operation is used (cell search for example).
Allow including identity in sequence by changing the value of sequence initialization. For example, pilot sequence in LTE is 31-length Gold code which is reinitialized at the start of each OFDM symbol with a value that depends on cell id.