Are you asking why you should seal it, or why you should seal it from the outside? – Tester101♦Feb 18 at 17:53
@Tester101 Why from the outside? And not from the inside which would avoid the water from getting "in" the door. – DrDroFeb 18 at 18:33
Have you tried contacting the manufacture's customer support? They will likely say to "do it the way we tell you" but it is possible they could give you their justification. – auujayFeb 18 at 21:53
Do they supply the sealant? If not, my guess would be that they don't know what type you'll use. So they say apply it on the outside, and wait 24 hours to shower to be on the safe side. – Tester101♦Feb 19 at 17:22
I agree that it seems odd. I googled "please seal from the outside" and found an instruction manual for their sliding doors, where they emphasize the same point. They also specify silicone sealant, so I don't think it's a question of what kind. To auujay's point, the manual also says their "Shower-Team" can answer any questions, and they provide an email address. – Tim BFeb 26 at 12:31