I'm sure somewhere this has been discussed before, but my search results did not yield anything and on the plus side I think everyone could use a refresher.

In what situations and styles do you designate crusting buttercreams, egg white/all butter buttercreams, ganache, and american buttercream.

Now let me give some details so that we are all on the same page.

Crusting BC - any kind of all-shortening BC that yields a crusted like shall that can be softened at certain stages with a paper towel or misted to give a shiny look. Shortening in BC often leaves an unpleasant feel in the mouth, but increases it's resistance against heat and humidity.

American BC - regarded as a quick-whip recipe, american bc is a fast to make but almost always yields a high sugar taste, thick but creamy and maneuverable BC. Comes in all butter, all shortening, and a hybrid.

Egg white/ all butter BC - Swiss, Italian, and french BC are regarded as time consuming, but yielding a light, fluffy, softly sweet product that spreads easily and refrigerates into a solid state.These traditional BC are usually all butter made that give them a mouth melting taste but makes them vulnerable to high temperatures.

Ganache - a chocolate/whipping cream ratio that produces a creamy chocolate, able to be used as a filling and as a coating. The flavor is decadent and the product refrigerates in a solid state. Ganache is susceptible to high temperature and traditionally cost more to make then a BC.

With these characteristics in mind, do you use certain icings for certain project. I was making a sculptured cake and thought to myself "which icing would yield the best result for this?" but why not make a list about everyone's application of icings.

Here is what I would give each icing.
Crusting BC - For covering BC only cakes.
American BC - I stopped using it unless I get into a jam.
egg white - I use these cooked BC as fillings for my cakes. I also use them under bc/fondant cakes.
Ganache - when the bride requests a very flavorful cake and is not that worried about pricing.

I would assume that cake layers that need to be sculpted should be filled with ganache? It refrigerates firm and is slightly more resistant to heat then butter? is this correct?

I never use crusting or American (no shortening ever and powdwerd sugar only in cream cheese). I use all European buttercreams including German, on all of my products except for Cream Cheese and Italian Meringue. Ganache is used when it compliments the product.

I have no trouble with the European buttercreams in hot weather. In 100% of these situations, the bride has opted for the cake to debut just before serving instead of being out for a long time.

I also use a full amount of buttercream under fondant.

You can lump crusting and American into the same category. Most recipes with powdered sugar are crusting recipes, regardless of whether or not they use butter or shortening. It's the ratio of fat to powdered sugar that gives the crusting effect, not the type of fat used. My American BC uses a combo of fats and is only very lightly crusting.

I use both American and European recipes. I don't really get into ganache much, except for the occasional cupcake.

I don't look at the project to determine what kind of icing to use. It's more about the "customer" than the project. American and European buttercreams are very different in taste and texture. However, you can do the same thing with a European buttercream that you can an American buttercream. The main difference of course is that with Euro BCs the consistency is manipulated with temperature as opposed to adding more sugar or liquid, like with an American BC.

Euro BCs have a more sophisticated and richer taste, in my opinion. The texture is silky and velvety and very good. You can use it for any kind of cake but it is especially appropriate for very special occasions when you want something with a more luxurious mouth-feel. American buttercreams work well for children's cakes or for the person who likes a sweeter icing. Again, what I use depends on the tastes of the recipient.

Regardless of which buttercream I use, they are both smoothed with a bench scraper. No paper towels, no rollers, etc. I don't have time or patience for all that.

I would say if you are sculpting, you can use either ganache or buttercream to fill. When you refrigerate buttercream it gets rock hard (think of a regular stick of butter in the fridge).

If heat is a concern, just tell the person to keep the cake in the fridge until it can be served. If that isn't an option, you might want to consider using a greater ratio of shortening to butter in your American recipe, or just use ganache. There is no way that I would use an all shortening recipe though.

Ganached cakes (covered with fondant) are never refrigerated in Australia

Ganache will certainly harden at room temperature, as well. (Refrigeration not necessary.)