Not that I work in this field, but I have heard the discourse from several people that string field theory is useless.
So I would like to ask two simple questions?
What makes SFT so difficult? Especially, it seems to me that one can construct an action that satisfies general coordinate transformation invariance and gauge symmetry (more precisely BRST symmetry) by using the BV formalism, as shown by Witten, but why is this useless?
When moving from QM to QFT has several practical benefits, for example, one can easily construct relativistic scattering problems in Lorentz-covariant form, but in what way is SFT superior to string theory?