The rifle is the direct damage weapon of engi and with SD it gets the option to magnify DPS by a large amount. With 30% reduced toolbelt recharge you can theoretically proc a static discharge every 3-4 seconds. You don't have the flexibiliy of toolkit or grenadekit for more utility or AoE condi spam but your damage comes very fast and bursty.

In the end rocket boots + super speed offer the best disengage in the game next to stealthing and propably the fastest way to travel between points next to a mesmer portal. Slick shoes is a nice CC for 1on1 situation or also to knock down a whole team if you need the CC.