Randomized trial showed improved success with US guidance
Constantinto et al., “Randomized trial comparing intraoral ultrasound to landmark-based needle aspiration in patients with suspected peritonsillar abscess”, Acad Emerg Med 2012; 19: 626-631.
Here is another example of a procedure that is somewhat uncommon, could be considered looking at fluid, but this is using what we call the endocavitary probe, be careful not to call it the endovaginal probe because we are putting it in the mouth in this case to visualize a peritonsillar abscess. In this case, you can see a complex structure that is fluid filled with some septations and in the far field you can see the vasculature including the carotid artery that you obviously don't want to put a needle in. There has been a randomized trial that shows that using ultrasound guidance for peritonsillar abscess will improve your success. It can tough to do dynamically, but I will often use this to determine where the abscess is, if there actually is an abscess, and how deep it is, and make sure I'm not going to inadvertently puncture the carotid.