Time-delay and source-redshift distribution for 202 investigated mock LSNe Ia for “LSST only” (upper panel) and “LSST + follow-up” (lower panel) for observing strategy kraken_2044. For a quad system, just a single delay is shown, either the first successful measured time-delay or the maximum of the six possible time delays. The blue circles show all 202 investigated systems and the orange filled dots correspond to systems where the time delay has been measured with accuracy better than 1% and precision better than 5%. Comparing the two panels we see significant improvement going from “LSST only” to “LSST + follow-up”, which we find for most of the observing strategies as suggested by Table 4.