  The aim of this white paper is to discuss the observing strategies for the
LSST Wide-Fast-Deep that would improve the study of blazars (emission
variability, census, environment) and Fast Radio Bursts (FRBs). For blazars,
these include the adoption of: i) a reference filter to allow reconstruction of
a well-sampled light curve not affected by colour changes effects; ii) two
snapshots/visit with different exposure times to avoid saturation during
flaring states; iii) a rolling cadence to get better-sampled light curves at
least in some time intervals. We also address the potential importance of
Target of Opportunity (ToO) observations of blazar neutrino sources, and the
advantages of a Minisurvey with a star trail cadence (see white paper by David
Thomas et al.) for both the blazar science and the detection of possible very
fast optical counterparts of FRBs.
