Sure, you can do that, depenidng on the purpose of the study. If we need the liquid culture for more qualitative growth experiments and if strains are sensitive to  washing  during preparation of an inoculum from a liquid culture, we directly inoculate.  If you suspend the agar picked colony and thouroughly mix, you can even obtain the same starting cell concentration in parallel incubation. However, the agar plated cells should be fresh grown, e.g. 1-2 days depending on the species.