Baneful magic altar on the same altar as other work?

I noticed that a lot of people have said you should have a separate altar for baneful work but why is that? What if you cleansed your altar after every time of the work you just did? Like sageing it and whatnot.

Depends on the system you are using. With the one i practice from black magick of ahriman rituals of benefit and bane are done with the same alter.

Completely depends on the system. Like in vodun having same alter is a big no no. It will kill you. But in angelic architect, demons included , I don’t think it will hurt .