Insight You've Gained by Playing Different Jobs

[Kasathar]

I honestly think that everyone without exception should play a tank and a healer at least once, to understand how the rest works. That's really how I gained a lot of insight.
I also have gained a lot of knowledge in regards to synergy in between certain jobs and created macros to ask for what I need depending on the situation.

[Lemuria]

Tanks need to stand still, so melees can hit mobs/do positionals.

Not entirely sure I agree with this one, but for one sole reason. Getting hit by strong AoE isn't generally wise in any circumstance. A smart tank will be able to move out of the attack range and slide back into position while their attack animation plays out, both avoiding the damage AND keeping the mob relatively stable. At least, that's what I do.

This way you both minimize the damage, which is a tanks primary job, and make things far less bothersome for positional attacks from your melee.

[Staris]

Learned - Lots of people are very unmotivated, and lack imagination.

[Able]

I main WHM. Playing WAR/PLD has definitely made me a better healer. I understand how their cooldowns and mechanics work much more. So, I'm more aware of when to be more conservative with healing potency or when I need to blow cooldowns and use more mana-intensive heals.

[Kazumac]

Playing a melee dps teaches you that tank spinning-top syndrome is bad.

[Lemuria]

Playing a melee dps teaches you that tank spinning-top syndrome is bad.

And also a potential cause of dizziness and nausea.

[Grey_Cain]

Got to 50 as WHM to try something different from what I normally do in other games.
Got DRG to 50 and realized playing a dps is always a lot easier than being a healer.
Got PLD to 50 and realized playing a tank is sometimes easier and sometimes harder than being a dps, but it's always easier than being a healer.
Queuing as a healer is always making things harder on myself, and more people should play as healers so I don't have to. :3

[Dragoon4life]

I stopped Healing and Tanking because

[kyuven]

This way you both minimize the damage, which is a tanks primary job, and make things far less bothersome for positional attacks from your melee.

This is part of why tank is one of my top 3 classes. While lower level runs can be like watching paint dry (during ifrit and Titan SM, I don't even technically have to MOVE while tanking) all the other instances have you moving more than most other classes...but it's not the OH GOD DODGE DODGE DODGE WHEW movement where you can cross the map. You have to move in subtle ways and then move BACK as soon as possible.
Honestly if you manage to get any of the tanking relics, you're pretty set for having some intuition as to when and how to dodge. I recommend doing so for anyone interested in raiding. It's not even that hard since tank queues are so short AND they usually get the in need bonus.

[Novaura]

I had always just focused on my DPS, starting with DRG and then NIN. It was only after getting my LV50 NIN that I started to make a PLD and a WHM. I can see why it is so tough to both Tank and Heal because you have to be so much more focused.