Proper Mechanic R2 Advancing

[BSUmp16]

My understanding has been that with R1 and R2 and less than 2 outs, on a fly ball to the outfield the PU will have the play at 3rd if R2 tags and goes. I have, however, recently been advised that in that situation if the fly to the outfield is routine (a can of corn) that the BU will take the tag at 2d and take R2 to 3rd if he tags and goes.

Is that correct? Do I have it backwards? Do I know what I'm talking about?

Any help would be appreciated.