Yes. As a lefty, don't show them the slice too often if you don't have to. This is similar to a good starting pitcher in baseball, if he has a good fastball he usually will throw it a lot the first time through the order so they don't get too used to the breaking ball and then he has that slider still in his back pocket.
The opponent will never get used to the wide slice completely unless he plays lefties regularly but if you can manage to use it a little more sparingly it will be even more effective in crucial points.
Unless it is indoor carpet, then they will never return the slice all day long

.
On carpet I like to hit a hard slice that only has a bit of slice (more like a cutter than a slider in pitching terms). That one is really deadly and I often manage to get to tiebreakers on carpet against people half a level better than me that eat me 6:1 on clay.