I have been long arming for two years now after being an avid free motion quilter on a sit down machine...I would say...

Pros:
- No Basting
- Easier to keep your quilt square, when FMQ we tend to squish our quilts out like a pancake
- TEN TIMES FASTER and personally once you get the hang of it, a lot easier than sit down quilting
- Better visibility when quilting
- Opens up new possibilities for quilting designs

Cons:
- Learning curve, it takes practice even if you are great at FMQ
- Financial investment (though there are economical options available)
- Standing to quilt/Space

I think it was worth it a million times over. That does not mean switching to a long arm was easy peasy and without some headaches...but I love it! :)

I like my long arm for all the reasons given and as to the standing part, I too have a chair on wheels - an office chair that I raised to full height that I can scoop along the rails. It enables me to see the quilting up closer.