Deinterlace Decomb

"Should Deinterlace and Decomb be used when exporting interlaced footage?"

It depends.

If the exported main file is meant for playback to broadcast or cable (NTSC, PAL, SECAM, or ATSC) or DVD-Video or BD-Video (Blu-Ray), then no.  That movie file should be interlaced, something like 480i60, 480i50, or 1080i60, 1080i50.

If the exported main file is meant for anything else (web, mobile device, social media), then yes.   That movie file should be progressive with any interlaced source de-interlaced .  So, the resulting file would be something like 480p30, 480p25 or 1080p30, 1080p25.

Premiere does not have a decom feature.

You should read the Handbrake manual.

Moved to the Video Lounge.