I'm sure you'll get a lot of advice, but here's mine:
First, the hair consists of an inner *cortex* and an outer sheath called the *cuticles* - cuticles are like the scales on a fish and on healthy hair, the cuticle will readily *open* and *close* and ideally you want the cuticles close shut in order to seal in nutrients and provide shine. Relaxed hair usually has uneven/damaged cuticles because relaxers (and other chemicals like color treatments, perms, etc) *eat away* at the cuticles, leaving *holes or gaps* on the surface with means that the cortex cannot retain nutrients becuase they *escape* out thru the the gaps in the cuticles, hence the propensity for dry, frizzy hair. Using low pH products helps to keep cuticles closed shut and using silicone based serums can help too, if properly used.
Serums help to *seal* in moisture as well as temporarily repair and fill in the holes and gaps on damaged hair. Most, if not all, serums contain silicones and folks either love um or hate um. I use to hate um until I learned how to use -- for me, only on WET hair immediately after my leave-in when I rollerset. If I put 'cones on dry hair, my hair becomes limp and loses body, so only on wet hair for me. Also 'cones cause buildup which MUST be removed periodically -- hence the need for a good clarifying 'poo -- and depending on how heavy-handed 'cones are used, must *clarify* every couple of weeks to every couple of months -- I find I must clarify every six weeks or so because if not, the 'cones *seal* my cuticles shut AND buildup on top of hair, preventing moisture, proteins and other nutrients from entering the inner layers of the hair where you really need them.
So you see the advantages and disadantages. On the one hand, you want to seal cuticles shut after a good treatment, but when it's time to treat again, you want cuticles to open so treatment can penetrate, not just sit on top of hair as it will if 'cones aren't eventually removed. Clarifying 'poos opens up the cuticles but they have advantages and disadvantages too: on the one hand, they effectively remove buildup and cones, but on the other hand, they have very very harsh detergents and can strip hair if used too often. So, its a delicate balance.
For rollersets I apply leave-in on wet hair first (nexxus headdress, salerm or giovanni direct) followed immediately by serum (nexxus glaze) and then I rollerset, using distilled water to re-wet if necessary. Once my hair is dry, I finish with a few drops of oil (jojoba, castor, nexxus botanic oil) mixed with a few drops serum. Always comes out light, bouncy and shiny.
Long post that I hope helps.
