Are reconstruction filter always needed? in mixed (digital and analogue application) where you have to convert a signal from continuous to digital time domain and then back again to continuous time an anti-aliasing LPF is needed and in general also a LP reconstruction filter.

Are there some applications (if so what are) in which the reconstruction filter is not needed or not strictly necessary?
If the system naturally has only a low enough frequency response (say a very heavy object relative to the forces involved), and the noise tolerance is high enough, then the effects of any aliasing, due to the lack of any additional low-pass and anti-aliasing filtering, may already be rolled-off below your desired or required noise floor.