That's a good point. Many of us on this board seal in the moisture with an oil and/or serum, which contains silicones. I've never experienced build-up from sealing in my moisture with oil after my leave-in. I rarely need to use a clarifying shampoo. Also, after it has been sealed, it doesn't necessarily last from one day to the next. I moisturize my ends, for example, in the morning and before going to bed. I also wash my hair twice each week, which could make a difference.
I'm just learning about silicones. I stayed away from them all this time because I heard it causes a lot of build-up on the hair and one must clarify often when shampooing. I didn't want to go through all that.
However, I learned all products with silicones are not alike.
There is a thread I started called Aveda Brilliant Serum where some wonderful ladies here shared their experiences with it - all great experiences. I did my own research also and finally bought some.
This particular serum does not build-up like many serums do and the silicones in it add lots of shine and eliminate my frizz very well. It happens to contain natural oils which also help seal in the moisture and condition the hair.
Thank you for starting this thread. I'm still learning what silicones does for our hair. For the most part, it sounds like it's beneficial.