This macro will not work the way you described. If you have an enemy or no target selected, any healing ability targeted on <t> will trigger a self-heal for the caster (Eos in this case). What is happening in battle is if the tank is below 80% when embrace comes available, she is auto-casting on the tank. When the tank is above 80%, Eos is actually healing herself when you use that macro. You don't have to take my word for it: go out and test it.
I use creative targeting macros for my attacks but never for heals. My approach is to have the tank be my target and use focus target to stack all my DoTs and bane on a single enemy. Example:
/micon Bio
/ac Bio <t>
/ac Bio <f>
/ac Bio <tt>
For attack skills, I agree 100%. For Physick and Adlo, I was originally of the same opinion until I learned more about how faeries operate. I have Embrace macro'd into those two spells, but not for the reasons everyone else does.
My reason is the bugged 20y radius for auto-healing. If any allies within 20y are below 80%hp, you have zero control over Embrace due to auto-healing and everyone's arguments for and against such macros are all moot points. If everyone is above 80%, I won't cast Physick or Adlo: I will just manually command Embrace if someone needs healing. Outside of 20y, however, Eos will sit on her hands and watch your allies die if you don't command her. The natural response to that situation as a player is to manually cast Embrace along with my own spells at long ranges. Putting Embrace together with Physick simply does what I would be doing anyways and gives me one less thing to think about in battle.