Raising combat skills on an ALT(ernative) character

Is there a good reason to level non crafted related skills on an alt?

I understand the benefits of having alt characters in order to use their islands to produce resources and then spend focus on them.

I also understand that if you want to be more or less self sufficient, having dedicated alts to gather and refine materials could be beneficial, since you can dump your learning points on those skills.

But is there a good reason to raise the combat related skills on them, instead of simply switching up your main character's equipment and do it with him? I'm asking that because yesterday I spent most of my day playing as a healer on one of my alts (and raising combat skills my main character doesn't own himself), but in hindsight I feel like I should've just spent that time on my main, even if those skills won't be immediatelly useful to him.

Any thoughts on that?