If the GOP convention goes past four days, the logistical problems are going to be an issue:

First the hotels:

The Republican National Convention is scheduled for July 18 to 21, but many party people are “booking hotels past the 22nd and 23rd” in preparation for a contested convention, the source said.
…
The RNC has blocked out most hotel rooms in Cleveland since last year, but some hotels may not be able to guarantee space after July 22 since they have weddings and other social events booked.

Convention planners have discussed extending their reservations, but have not made an official request to Ohio hotels, an RNC source said.

Then the police:

A longer convention with more national and international interest would be good for local businesses supplying the event. But Cleveland’s police union president, Steve Loomis, says it would put added strain on officers providing security.

“We’re going to be stretched as thin as you can possibly be stretched during the scheduled convention, so that would be bad news for us; we would not like that. These guys are going to be on 12-hour shifts in very difficult situations, very stressful situations in the middle of summer, so that would not be a good thing for us.”