This question comes up often. IF YOU HAVE SLIDE LOCKS, THE OEM DETERMINED THEY WERE NECESSARY. Slide locks, depending on the type slide room and mechanism are required. Some pull in the top flange to get a positive weather tight seal(Newmar is one as a LOT of others). Some pull in to keep the room from vibrating and moving(not extend but wiggling) in transit. Regardless, the OEM's would NOT build/pay and install locks if they were not needed. They are rarely used to stop extension in transit. Not all slide rooms require locks, but if you have a unit that has them, then use them. Doug