Rule 50(a) motions are truly the stuff of nightmares. If you are unfamiliar (experienced trial attorneys can skip the next two paragraphs), almost all patent cases involve post-trial briefing, where the losing side seeks judgment as a matter of law on the basis that no reasonably jury could find for the opposing party, even though that's exactly what the jury did.
Post-trial JMOL motions are not throwaway motions. Parties actually win them. And if you don't win your post-trial Rule 50(b) motion, what do you do? Appeal and try again, based on the arguments you preserved in that motion. These motions are critically important—albeit, only if you lose at trial.
But the post-trial Rule 50(b) motion for judgment as a matter of law is actually a renewed motion. To include an issue in your Rule 50(b) motion, you have to first make a 50(a) motion on the issue, and that motion must be made before the case is submitted to the jury. Otherwise, the issue is waived for post-trial briefing.
The problem, of course, is that you have to make your Rule 50(a) motion at the exact moment you are most stressed and concerned about actually winning the trial, when the motion feels like a giant distraction. And you have to do it knowing that you will almost certainly lose the 50(a) motion. The point is to preserve the arguments, not to win.
Trial teams handle this many different ways, but the most common seems to boil down to ...