I find using macros like:
/ac physick <mo>
/ac physick
To be very risky. If you miss your mouse-over it will either heal your current target or yourself. There is no way to distinguish the heal's target before it fires. FFXIV is prone to crappy mouseover detection and you will often find your heals firing on the wrong person (which will get you wiped in savage).

I haven't checked but assuming you can disable auto self-target, it would be much safer to use <t> on the second line. This requires that you target the boss / enemies at all times. This way your missed mouseovers will not cast on the wrong target and you can actively see the bosses casts without needing to focus-target them.

Some people will tell you dont use them because of queueing. This is mostly applicable to DPS classes (and your dps actions) where you will lose an enormous amount of dps for not being able to queue GCD actions. At times where healing is extremely intensive, not being able to queue heals could be a problem due to having lower burst output.

All a matter of personal preference, but if you can get used to the 0.1s it takes to click the person you are already mousing over, it's better... especially if you can spare focus target for the boss so you can see the casts.