jump starting can cause your ECU to be damaged due to transient voltage spikes, even with the correct polarity, the flatter the battery the larger the spikes. my brother had his supra mk4 in for repair and they kept jump starting it, the replacement ECU 2nd hand was £650.
most cars have a reverse polarity fuse, but this only protects the wiring, anything which carries the current, fuses only protect wiring, they cannot protect the load, a spike can get through the fuse in a split second before the current melts the conductor in the fuse.
there is an element of luck involved and somtimes you can get away with it, you should have difficulty connecting the leads the wrong way so the voltage sparks should stop you quickly and limit the potential damage, as a general rule the resistive loads will be ok as they are not polarity sensitive, but any solid state items are at risk, in particular the full bridge rectifier in the alternator.
the battery does not care as it's worst failure mode is heavy cranking very high current flow over time which can distort and short out the plates. hope this helps. herbiemercman.
