Only selected decoder, but remember, even if the decoder has hdmi enabled, the output still in standard definition.

Exactly, the satellite broadcast signal still in SD for NJOI channels.

The benefit of using HDMI (if enabled on decoder) ; only one cable is used to carry audio and video, less cable cluttering around.

Not to mention since HDMI signal sent to the TV set is digital, so there is not dot crawls issue.
Except if the broadcast itself is still analog (such as media prima channel ;TV3, 8TV, NT7), you still notice there is dot crawl even with HDMI connection.
I think Astro actually receives media prima channel (analog composite signal) using the normal antenna, then encode to MPEG2 before broadcasted to the satellite.
With Astro own digital broadcast (such as AEC, astro awani etc), no problem with dot crawls.

(The analog YPbPr also eliminate dot crawls, but it uses too much cable)
(Really? 3 cables for component video signals and 2 cables for left+right audio?)