But then you lose the ability to have your reply to be from different accounts. At least that's how I understand it.
You can manually set the "From" account for each mail in Mac Mail. Also note that "From" and "Reply to" can be different. However, I recommend one main account if possible, or a main personal and a main work. I have four active mail accounts, but only one account that is 99% of my email. Very few people are paid to be email experts, and I'm not one of them.