You are correct. Cost would be the only reason not to have high flow. On my TC 5610, it has to have high flow to run the rear pto.
There is a high flow button on the dash. If you don't need it, don't push it. Many attachments cannot take the high flow rates and could damage the attachment. On other attachments, it is really useful to get the best performance. It would be difficult (if not near impossible) to add high flow later.