Never needed it with my blader, just like a tank, but with pure int, it is usefull to switch to shield to block the attack and give them a nuke with spear
lvl 5x Hybrid Blader lvl 90 Pure Int S/S lvl 7x Rogue/Cleric
I have always had trouble switching weapons even with them placed on the bar. More of a lag issue then anything else I think. I doubt any macro would help with that, I would think the timing issue will still be a problem. Don't forget your floating bar that makes things easier as well.
lvl 65 4gap 84:84 bow inactive. GOLD GUIDE Just Read It
I would recommend using the extra floating bar, so you don't clutter your main bars "F1 - F4". to use the extra hot keys on the floating bar press: "space bar + corresponding hot key"