The following is a great example from Ricardo Urtubia showing how effective laryngeal manipulation can be in exposing the larynx. Note that in this case, once ELM is taken off, the laryngeal view is lost. This may be because the patient was not optimally positioned first with head elevation and ear to sternal notch positioning. Often, as mentioned above, ELM will seat the blade tip optimally within the valleculae to engage the hyoepiglottic ligament and lift the epiglottis indirectly and allow a good view without the need to continue to maintain ELM.
[Update 2016-08-10] Ricardo further points out his opinion that ELM stabilizes the laryngeal complex to assist tube delivery into the trachea and thus should be maintained by an assistant.
On further thinking, this makes sense to train one’s assistant to practice this and do it routinely especially for those cases where ELM must be maintained for optimal laryngeal exposure and may be helpful for a difficult tube delivery (small spaces, larger ETT, hyperangulated indirect (“video laryngoscopic” or VL) approach etc).
The only downside of maintained ELM is when it is applied blindly (usually under direct laryngoscopy only (DL) circumstances), the exposure may become suboptimal or too much pressure is used and hampers tube delivery. VL/DL combination and trained/briefed assistants can avoid this issue.