What a timeline gives you that basic merging doesn't
Plain clip-merging tools play whatever files you provide, in the order you arrange them, with no adjustment to the clips themselves — a timeline-based joiner adds the ability to trim each clip's in and out points before they're combined, so you're not stuck using each source clip in its entirety. This is the difference between quickly stitching together whole files and actually assembling a sequence from the exact portions of each clip you want.
For anyone building something more considered than a straight back-to-back combination — cutting out a bad take mid-clip, using only the relevant seconds of a longer recording, arranging pieces from several sources into a coherent sequence — a timeline is the right level of control without needing a full video editing application.
Trimming in the timeline vs. trimming beforehand
Trimming each clip directly within the timeline before final export means you can see and adjust the whole sequence in context — how one clip's ending flows into the next clip's beginning — rather than trimming clips in isolation and hoping they work together once combined. This contextual view is genuinely useful for getting pacing and transitions right, since a cut point that looks fine on its own can feel abrupt or awkward once it's actually next to the following clip.
Mixed source formats still need to be reconciled
The same format-matching consideration that applies to simple merging applies here too — clips with different resolutions, frame rates, or codecs need to be reconciled to a common output format, which can introduce a visible quality or aspect-ratio shift at clips that don't originally match. This is worth checking before building out a full timeline, since discovering a format mismatch late means redoing trim points against a different combined result.
This sits between simple merging and full video editing
A timeline-based joiner occupies a useful middle ground: more control than basic sequential merging (trimming, precise placement) but without the complexity of a full editing suite (layered effects, color grading, advanced transitions, multi-track compositing). For assembling a sequence of trimmed clips into a finished piece — without needing the deeper toolset of a full editor — this middle ground is often exactly the right amount of capability for the task.