As Jur says it depends on the bike and the quality of the suspension. I have test ridden a Dahon Jetstream EX with dual suspension, the front forks being German A (€900 suspension0 and it works beautifully and is fully adjustable. Adjustable suspension means you do not really have to employ it on smooth roads but it comes into its own on rougher surfaces or trail riding.

I had Schwalbe Marathon Apple tyres on a Dahon Cadenza 8 and they acted very effectively in absorbing vibrations on rougher trails but it did help that the wheels were also 26".