Do you need to? No. But I do have accounts on both and will keep it that way, because they’re just completely different experiences and Kbin isn’t to a point yet IMO to fully replace Mastodon on the client level.

I had a completely separate reddit and Twitter username for a reason. In fact, the username I used on reddit was not used by me anywhere else.

I plan to keep it that way in the fediverse. Reddit-like instances will use one username and other platforms will use something else.