Aparently on the Byron F-16, they do help the slow speed performance..and that thing can fly incredibly slow at a very high alpha. Never noticed much of a difference on my Tamjets, 'cept that it looks cool.

Underwing pylons, on the BVM F-86 (small one) they help directional quite a bit..it really grooves with them and the tanks on...plus they protect the belly in case of a gear up....