Just to be clear (as I have no experience with Mentor at all so you can tell me anything): what you are after is that if you move a symbol the connections will rubber-band along without creating connections that shouldn't happen. If yes, then I think that is a usefull feature that can prevent costly mistakes.
Yes, that's just one case. Since when you connect a wire to a symbol pin,
you're actually connecting
a wire to a symbol pin, schematic capture is aware of the connection, and the wires rubberband as
you move the symbol. Often that movement will cause wires to intersect with other pins, wire vertices,
etc., which might have the appearance of being connected. But since they're not (according to the
netlist and the fact that
you didn't explicitly connect them), they get flagged as crossings for you
to clean up. As I've explained a few times, the action that drew my attention to this problem in KiCAD
was doing the simplest of symbol edits - the library 555 is really odd in terms of which sides the various
pins are on - at very least, 2,6, and 7 are generally accepted as being on the left side and 3 on the right.
So after sorting it out in the symbol editor (which was nice to use), I returned to the schematic and
instead of finding the right wires rubberbanded to the right pins, the wires were now misconnected to
the pins I'd moved. Is this a dealstopper when you're editing an 8-pin symbol? Of course not. But if
it's a TQ144 CPU or a PQFP208 FPGA or a 1000+ pin BGA, that can be a mess.
I'm a long time Orcad user and I can tell Orcad doesn't do such checks so you have to be carefull when moving components in order to keep the connections the way you intend. The old DOS version was even worse. When I was an intern at an electronics company they had me create a PCB layout from a netlist. Once the PCB was assembled & being tested the electronics engineer started giving me a lot of flack for making a mistake in the layout. Having quite a bit of layout experience at that point already I was quite sure I didn't because the DRC check wasn't showing any shorts. Long story short, it turned out the engineer had moved a component and DOS-Orcad had screwed up. Instead of 2 lines crossing, both lines where taking a right turn and thus making the wrong connection. This was not visible on the schematic at all! The same circuit was repeated 16 times on the board as well so there was quite a bit of rework involved. Modern day versions of Orcad automatically place a dot in such situations indicating a connection between the lines (and put them into the same net). You could succesfully argue that this leaves checking the schematic for continued correctness with the user.
Sounds like you have a pretty good handle on the kind of problem I'm talking about. And I would
absolutely agree with you that adding the dot is exactly the wrong way to deal with it - assuming
that because two wires are crossing they should be connected, so quietly just taking care of that
for you? What the hell were those people thinking? The behaviour I'm describing would put a dot
there, alright, but a
red one indicating: Buddy, you've got something here to sort out.
[edit]
Worth adding that the system I'm talking about doesn't flag
every crossing, of course. That'd
be a makework PITA. It just flags the ones that are more likely to be mistaken for valid connections,
such as a line crossing a pin, vertex landing on a pin, vertex (or end) touching a line, etc.