Just so you know, to save the amount that chmurf is talking about is rare, particularly on a 1 or 2 night stay. We stayed at RPR in October - 2 rooms for 3 nights and saved probably a total of about $150.
absolutely. It does not work for everyone or for every type of stay
so let me talk about our specific case.
we're staying onsite at OKW for 3 weeks.
During that time, we will spend 2 nights, one at HRH on week 1, one at Portofino Bay on week 2. We'll be taking advantage of the fact that 1 night at Universal gets you 2 days of unlimited express passes and early entry (check in and check out day)
on week 3, we are looking at level 2 attendance, so we'll go without express passes.
So that's 2 one nighters while we'll still be checked in at OKW
At Portofino Bay, rack rate price for 1 night for our dates, for a 2 queen bay view is $364 (before tax)
Annual Passholder rate for that night is $239
that's a saving of $125 for that night alone.
we could also opt to book a Club level room for $334 (yes cheaper than the bay view without AP)
At HRH 2 queen pool view, $334 and only $229 with AP discount
that's a saving of $105
for those 2 nights, if we book a bay view at Portofino and a Pool view at HRH we save $230 on rooms alone. (we could save more staying both nights at portofino and booking standard view)
for each visit in week 3, we save $18 since we get free parking with the preferred AP
and we get 10% off food and merchandise.
preferred pass costs $335, we will save roughly $300 with the AP (between accomodation, food, merch, parking at parks on non hotel visits as AP does not get free parking at hotels) so that brings my ticket down to $35.
Now this works for us because we chose to stay checked in at OKW and pay the Universal room on top of our WDW booking. This saves us packing, and we keep free dining throughout our 3 weeks stay.
For guests who will make 2 separate stays, like 1 week WDW then 1 week universal, it might not work as good.
for example, a 4 nights stay in a 2 queen pool view at HRH at the same period of time will cost on average $267.20 a night with the stay more, save more deal (room only)
that's $1068 for the 4 nights (excluding taxes as I don't factor them in any of the simulations here)
the same stay, with AP discount averages $229 per night for a total of $916 pretax.
that's still a saving of $152 before tax on that 4 nights stay.
if the guest's stay does not fall inside the blackout dates, they could go for the power AP, which is cheaper at $228.27 (including taxes, and without shipping = will call)
so with the AP discount, the power AP comes at $76 which is still way cheaper than a 14 days bonus ticket
and the preferred AP comes at $180 (with food and merch discounts on top) which is still cheaper than the 14 days bonus ticket.
But this does not work for every stay. We go at a "slow" (regular as per Universal's rankings) and the AP discount is deeper than it is a peak times. So it's not as worth it at busier times.
there is also a caveat. You are supposed to have an active AP at check in to qualify for the AP rate, so depending on how lenient the Team member is at check in, you might have to go to the parks and enter them to activate your AP before checking in (most TMs will allow you to show your AP at some point during your stay)
also, AP rate must be booked, discount cannont be applied after the booking is made.
if you want to make a simulation, go to universal, click on onsite hotels, and select "promotion", then type APH in the code box.
AP rates are usually available 3 to 4 months out, so nothing will show for later dates. and if nothing shows, then nothing is available at that rate.
Every penny counts 
