I've never done crane work, but...
Ddrt for adjusting up and down many times (climbline style) and work positioning (lanyard style, either on the bridge or on the Ds).
Ddrt for traversing ( leaders or trees), either for pulling if your travel has to be close to horizontal, or for releasing to recover the line easily from the previous TIP. Same for pulling yourself along or under a long limb, instead of limbwalking.
Ddrt to retrieve a remote high TIP (primary or secondary) if you don't want/have to go back up there.
Srt for access, long travel, choked line at long or close range, tall trees for the emergency exit, multiple successive TIP (bunch of spindles trees or tall sprouts, wide crown).
All that could be found in a single job.
That's why it's so usefull to have two climbing systems, each able to swap at will from one to the other style.