Originally Posted by Cubdriver

An airline pilot may wish to comment on this because they fly only IFR and would know more about real world practices; but I think if you are cleared to intercept a particular DME arc by a controller then you may do so, and you do not have to fly to one of the two llustrated IAFs on the arc if you have the clearance.

Originally Posted by TheGreatChecko

ATC will clear you to a fix.

ATC cannot just let someone fly where they want, they need to ensure terrain clearance and separation. A DME arc is just another type of transition to an approach and like all transitions, they have to be started at an IAF. ATC will clear you to the IAF and if you are in a non-radar environment will clear you for the approach from that IAF. Also, if the arc IAF isn't convenient, there is probably an easier transition closer to your position anyways.

In the training environment, we create arcs just so we can practice, so essentially we intercept them wherever we want. The only difference between that and "real life" is that point at which you intercept the arc has a name and you would fly a radial to that point and then intercept the arc exactly like we practiced when getting out instrument rating.