if the day you are going to universal has the express pass for $15 per person, wait before you buy it. when the charges are low for it, it is an indication the crowds won't be there on that day.
go before the park opens. do as much as you want or can by 11. 11 is when the crowds start to come in. if you think the lines are too long at that point, then buy the express pass. why pay for them if you don't need them?
they are only good for one time only per ride and attraction.
they are only good for the park you are in .
say you start the morning at 8:30 in IOA. you finish it by 11:30 then stop to eat. go over to the studio side and do rides/attractions there. if the lines are long, buy the express pass then.
i don't think you will have crowd trouble. go to uo on a weekday and eat at off times to avoid lines and people.
the cost of the express pass is determine by what day you buy it.
when parks are open late to 10, the price is higher.
it is the same price as on line in advance as it is if you buy it at the park the day you are there.
some people prefer to line all their ducks up before a trip. they want to have covered all costs and have plans set, therefore, they buy the express pass in advance.
wait to buy the pass when you are in the park.