I find regen great on certain characters, mainly Deande, Mellka, Alani, and Miko. When playing a tank, that regen isn’t going to get you very far since you should be soaking up damage and Max Health or Damage Reduction would serve you better. As for why I enjoy it on those characters, it helps with their survivability.
Deande can be dangerous with Calculated Risk, which also leaves her open to damage to her health before she can escape, so health regen can patch up the little damage she took without having to move to a healing station, returning to base or needing a healer.
I play Mellka more as a harasser than an assassin, I tend to attack and do a respectable amount of damage and retreat before it becomes risky. I would prefer to make two or three enemies retreat and heal instead of focusing one and killing them. With that in mind, I stack max health to keep me in the fight longer and health regen to get me back in the fight faster without having to retreat to heal.
And as for Alani and Miko, I love it on them so I don’t have to worry about needing to heal myself a much. Alani’s self-heal is bad compared to her ability to heal others. Her wellspring is barely noticeable on her and her riptide heal is bad in general, while her geyser is great but is better off being used on a wave of minions. While Miko can heal themselves from Level 2 right helix, Heal Thyself, but that takes away from her left helix, Regenerative Aura, which I find nice for a nice little heal for a wave of minions and helping other nearby allies that you are not healing since another one is in more of a need for it. Otherwise, you have Biosynthesis, which I prefer to save and use when healing an ally in a bad situation.