not really unless your plastering or have a tile joint running through there would usually be a batton running through which your adhesive will fill upto
i'd normally scrim the joints, and if it's feather edged board, i'd flush with bagged addy, then let it dry before tiling. and flexi addy for plasterboard too.
Tape them, then skim a bit of addy across the tape when I'm tiling. It's to stop hairline cracks when skimming, not sure its that necessary when tiling, can't do any harm though. Better safe than sorry, don't want a crack appearing cos you didn't tape a joint!
the joints should definately be taped!
as you tile, then the adhesive will act as a skim coat anyway, so it all helps with regards to the overall bond and strength of the substrate.