There's no need to do partials to strengthen the tendons and ligaments. Heavy full-range movements do that just fine. Partials can be used to work specific areas or weak points in the full lifts though. For example, board presses can be used to train the lockout of the bench press or rack pulls for targeting certain areas of the deadlift. I don't think partials in the squat are really beneficial for anything I can think of. Like most things, when used correctly partials can serve a legitimate purpose and when used incorrectly can cause problems and injury.