Just as Romeo and Juliet follows the stories of Romeo and Juliet, Shakespeare in Love also has two plots for its two leads: William and Viola. No confusing flashbacks here. The film is chronological and easy to follow as it flip-flops between both protagonists. Most of the time they're onscreen together anyway. Unlike a Shakespeare play, this one needs no narrator to tell us what's going on. It has plenty of montages to do that for us.
Montages: The Capulets vs. the Montages
Maybe screenwriters Tom Stoppard and Marc Norman made a typo in the script, and instead of writing "Montagues" they wrote "Montages" … and the director took it literally.
This movie often uses the montage for a variety of purposes—to show the passage of time (most of the movie takes place over about two weeks), to show hot hot lovemaking, or to show actors rehearsing for a play. There's nothing more boring than watching people say the same lines over and over again, so we're glad those montages speed things up a bit.
And who could forget the prayer montage, as Will prays and almost flagellates himself feeling guilty over the death of Marlowe. Because this is a romantic comedy, and not a tragedy like the play within the film, the filmmakers use montages to speed up anything unsettling or traumatic. It keeps the mood of the film light… but it also makes Will look disingenuous.