This is not a standard practice but a malpractice of desi mechanics.
when the engine head surface becomes uneven due to one of many reasons like over heating or uneven/over torquing by the mechanic. the head needs to be faced very slightly in order level up the surface for maximum even contact. It is to be noted that there is certain limit to which the head can be faced after that it is to be replaced.
The counter surface to the head is the engine block, if the engine head needs surfacing then there are 90% chances that the block also needs it.
if not properly done or over done by the lathe worker the over heating will not go away and also the timing belt will stay loose with standard tensioner.
Mechanic do this when they only face the head and not the block. they know that the standard gasket will not cover the difference between surface contacts and timing belt issue. So they use the double or two standard ones to fix this.
Get the engine head and block faced from a reputed professional as he will be able tell you the real story if the head / block can be faced further. then get a the genuine SGP head gasket. Be sure to get the mechanic who know the proper torquing sequence and has a torque wrench in order to apply proper and even torque to all 8 bolts. You will then love the results