I wondered the same thing. From the github link, I don't see the advantage of Lava over Verilog or VHDL, both languages designed for describing hardware. Maybe Haskell provides some compiler guarantees?
These are all valid points for high-level languages in general. One can add easier parametrization to the list (high-performing HDL code can be terrible to reparametrize).
I was mostly surprised by the choice of a Haskell-based DSL. I think such languages miss their target audience. Most people writing in an HDL are hardware designers without significant software training (I am fortunate to be a software-turned-hardware person). For them making the jump to, f.e. a functional paradigm (as in Bluespec), is much harder compared to a lesser, more popular evil (C/C++ based DSLs like SystemC or AutoESL).
- faster design time, as you write less code to get the same things done
- reusable high level specifications
- access to high level optimizations not easily possible on the VHDL level
- easier to formally verify the high level spec matches implementation
(Aside, I used to work for a company that designed and sold these types of toolchains).