i just registered a strange thing: there are "out-of-the-box" segments which are only available within the report builder.
for example, if you want to use the segment "first time visits" in a workspace, you have to rebuild the "default" segment on your own!
i vote for one of those solutions:
a) make those "default" segments available everywhere (what i prefer)
b) delete those default segments
btw: if someone knows the reason for this limitation, love to hear a word ... can't imagine any use cases ...
just get a hint that thos are Segment Templates
therefore i would prefer a 3rd option
c) offer function to hide "Segment Templates"
Segment & Calculated Metric "templates" are now shown in Workspace left rail by default. They can also be removed from a view through Virtual Report Suite curation.