I heard that when mixing a lot of DJs rub the platter or spin the label to keep the records in time, is this correct? Why would you need to do this when you adjust the pitch with the pitch control to get the records in sync.

cose no deck is 100% accurate on the pitch so its likley that u will have to end up correcting at some point during a mix to keep it in time.
some people touch the platter or vinyl to keep the tunes in time but most djs probably use the pitch

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From personal experience, touching the plater or label is more noticible. Using the pitch to make corrections is a little harder but once you have it mastered, it is probably the best way.

In trance in particular, sounds from tracks are often "there", that is they sweep and are able to be constantly heard. Cause of this if u flick the vinyl or brush it you're causing a big change in a short period of time, this becomes very obvious to those listening.

Pitch shifting is much smoother so changes you need to make arent as audable.