  Following the approach of B. Roberts, we characterize the non-vanishing of
global theta lifts for symplectic-orthogonal dual pairs in terms of its local
counterpart. In particular, we replace the temperedness assumption present in
Robert's work by a certain weaker assumption, and apply our results to small
rank similitude groups. Among our applications is a certain instance of
Langlands functorial transfer of a (non-generic) cuspidal automorphic
representation of $GSp(4)$ to GL(4).
