The body of an aircraft in simple planes is very rigid so if you have very long wings or many segments of wings they tend to flop around this is where is strut could come into play or if you want to hang heavy bombs off the wings it would help for rigidity even if they fix the problems with flapping wings I think it would still be nice do you have some struts
I use modded structural wings ever since I had built a few massive planes and the wing flapping was very annoying.
FullFruntall's idea is the best. It's pretty easy to find fuselages that are 0.1 or 0.05 tall/wide and you can fully adjust the length, rise and run.
There are two ways to get some kind of struts, the easiest and simplest is to use structural wings, the other way is to find someones design with a XML edited fuselage piece, download that, take the piece of the plane and save it as a sub-assembly.
Use thin wings and/or pylons