combine order, invoice, and backlog detail in one fact table

I am thinking of combining the order, invoice, and backlog detail in one fact table. They all have the same dimensions and level of grain. The total of the invoices = orders+backlog.

I don't see any benefit in having 2 fact tables. One with invoice detail and one with order and backlog(open orders) detail.

Do you see anything wrong with this?

Yes. An order and an invoice are entirely different things. You may consider creating an aggregate of the two, but I would not replace the two facts with a single fact.

Thanks!