When I want to joint segments in SDLXLIFF, the only way possible now is to edit the current source segment to add the content of the next.
Seg #1: This product is
Seg #2: easy to use
Then, edit Seg #1 to
This product is easy to use
and make Seg #2 blank or enter some personal warning for post-editing in Studio.
This is a good workaround unless Seg #2 contains one or more tags, which cannot be transferred to Seg #1.
So, my proposal is for CT to do this editing (in the background) by adding the entire content, including tags, of the next segment to the end of the current segment, and emptying the content of the next segment.
I guess this is different from simply "joining segments" and should be possible so long as the source segment is editable, even in the cases where segment joining is not permitted in Studio itself.