it you just backspin the outgoing track and suddenly slam on the incoming track it sounds shit, but if youve been mixing your two tracks together for 32 bars or whatever and backspin the outgoing track at the last second right before the inncoming track goes into a drop or a release/build section it can sound awesome. backspins sound best I reckon when its just a beat thats playing, so during the last 16 bars of the song in the outro typically. backspins while its mainly synths sounds fucking terrible.