IMO the quill is for drilling, not milling, unless access is difficult. Why increase the bearing loading and any machine errors (very considerably with the quill fully extended) by end-milling with an extended quill? Seems like a good way to reduce the life of any machine, so clearly (to me) is bad practice if used on a regular basis.
ER and Clarkson collet systems can, and do, certainly add considerable extra bearing loads when milling, without a quill extension on top of that. I always use the knee for height setting, if possible when milling.
A tilting vise could clearly be used for drilling at an angle, with a mill with no quill, although other means of work-holding are available to those that don’t have one. A tilting vice (or other fixing methods) could still be used even with a mill with quill – and especially necessary for those mills with a quill but without a tilting head!
In the absence of much prior consideration (of the possible alternatives), perhaps think of sine blocks, angle plates, tilting angle plates and simple packing pieces as alternatives to a tilting vise. After all, they are not need that often.