Butternut/squash soup: to roast or not to roast?

Both ways can be used, depending on your palate. Jus as Sarah rightly mentioned roasting gives you a caramelized flavor which enhances the sweetness while roasting and cooking it directly may tend to reduce this sweetness. This may not change the taste of soup much, however if you are really picky about the specific flavor and taste, please choose the cooking process accordingly.

I'd say no...sometimes the roasted squash turns out a bit----hummm, strong, burned, too sweet.
Instead of a smooth creamy soup.

I've done all the methods, and since I make a lot of squash soups, I'm glad to vary them from soup to soup. But the cut in half, roast, scoop method is the easiest. A lot of people really dislike peeling and handling raw butternut squash.

Meh... really depends on what you want at the end and also your roasting/cooking methods. I've long made butternut squash soup simply cooking chunks in chicken broth until the chunks had broken down so much they could easily be whipped with a whisk. More recently, I started roasting. First few roastings were simply cutting the squash in half and cooking upside down (really, almost more of a steaming). There was no discernable flavor difference. After that, I cut the squash in cubes, added some olive oil, S&P and roasted in oven. Slightly intensified the flavor, was much more difficult to blend (most difficult of the three approaches) and also added unsightly dark flecks from the crusts that formed -- it was a pain to strain them out. Personally, I've come full circle and will cook cubes in chicken stock going forward. The flavor difference is so slight it doesn't justify the extra work (and, FWIW, in my family, I was the only one who could notice ANY flavor difference).

I would absolutely roast the squash beforehand- it ups the flavor by tenfold, and does most of the work for you prior to blending the soup! A little olive oil & sea salt, some time in a hot oven- it really brings out the best in the squash.

Depends on what kind of flavour you want - it will caramelize more (= sugars) if you roast, and sweat more (= milder effect) if you just add it straight in. So you'll get more caramel flavour if you roast it. Both are nice

Roasting the squash first will definitely enhance the flavor of the soup