What are the effects of sampling time on digital control performance?

Sampling time affects digital controller performance through: discretization (conversion from continuous to discrete), aliasing (frequencies above Nyquist appear as low frequency noise), phase lag (sample-and-hold introduces delay equivalent to T/2), and computational delay. Guidelines: sample 10-20 times per closed-loop time constant, minimum 10x faster than process dominant time constant. Fast sampling wastes resources; slow sampling degrades performance. For cascade loops, secondary should sample faster. Anti-aliasing filter required before sampling (cutoff at 1/5 to 1/10 sample rate). Consider computational delay in tuning.