Sealing for me is essential. My hair is long and porous, and so I have to keep moisture in (and lock excess out in high humidity.)

Sealing usually consists of adding oil on soaking wet hair prior to adding stylers. I do mine over my LI.

I sometimes seal with jojoba or SM elixir, but my favorite thing to seal with is mineral oil.

You take a few drops of oil, and gently smooth and scrunch it in, concentrating on the ends.

I sometimes use oils (not MO!) on dry hair to smooth 2nd day hair or to add a little softness to dry ends. In the winter I'll sometimes do this before bed to help prevent moisture loss overnight, too. But I don't see oil on dry hair as sealing - I think that's really only sealing the moisture into you hair when it's wet/before it dries.
2c/3a/3b, Fine/med, Dense, high porous, & normal elas.

Lo-poo - Renpure Keratin, SMR, Giovanni SaS
clarifying - mix Johnson's H2T with low poo
Co-wash - Suave Nats. clar. or coco.
RO - GVPCB, Ion Eff. Care, TN.
LI - SMR, Cure Care, or RO
Seal - MO or Jojoba
DT - + honey, ACV, & EVOO to SM masque & GVPCB
PT - Gelatin!, CNPF
Styling - FSG, AIF, BRHG, LALS/PS, GF curl spray gel, SM Souffle/Smoothie, LOOB
Oils - MO!, EVOO, jojoba, GSO, SM Elixer, EVCO, VO5 Hairdressing