Pretty significant differences. Visio is a dedicated *diagramming* package,
that happens to include facilities diagramming among its abilities, hence
the architectural abilities. In that respect, it can do many things AutoCAD
cannot, and exhibits "intelligence" in areas like routing (in your case,
walls) and process mapping (etc) far superior to what AutoCAD, LT or
otherwise, can natively accomplish. AutoCAD LT is a general-purpose CAD
package that has strengths in graphical areas where Visio comes up short.
There is certainly some overlap between the two, especially in rudimentary
CAD functions, but I could never picture the two as interchangeable.
I much prefer Visio for architectural myself, simply because it's so
user-friendly. However, architectural add-ons for AutoCAD (not sure about
LT) provide some impressive advantages over Visio (especially where 3d is
concerned). Pick the one that best suits your purpose.
Randall Arnold