Different samples in the wavetable are used for the attack phase (at the beginning of the sound, as the volume increases) and release phase (as the end of he sound, as the volume decreases) of the sound. These are normally very difficult to synthesize with other synthesis techniques, but because these are stored as samples very realistic sounds can be produced with little processing power.
Because single samples are somewhat limited for synthesis of new sounds, modern wavetable synthesizers can combine multiple samples or even change the sound with filters.
Because of the low procssing power required early synthesizers imitated filters and other expensive synthesis methods by rapidly playing successive samples from the wavetable. If each sample is a little duller as the previous a filter effect can be imitated.
Special effects can be achieved by selecting a sample at random or in a special pattern from the table on a tempo-tick from a sequencer. But the effects are quite strong and don't sound very natural. Of course this can be used on purpose to give the sound a special "edge".