When I bought my first house I noticed that the switch in the master bedroom made a buzzing sound whenever I turned it on. I had planned to replace all the plugs and switches anyways because the house was built in the '60s and I figured that they were probably the original fixtures, but the buzzing confirmed the necessity to me.
Ever been to a hotel and tried plugging in your phone charger but the block just falls right out of the receptacle? Maybe you need to bend the prongs out a bit to ensure a good connection. This is the result of regular wear and tear for a hotel. Receptacles, like anything else, has a limited life span.
A bit of preventative maintenance is usually a good thing. Why wait for something to go completely wrong before you feel the need to fix it? When your dealing with electricity, maintenance becomes an even bigger priority. Circuit breakers are there for when there is a catastrophic failure of some sort, but there is usually a few things that can be done before it gets to that point.
When one switch in the house starts acting funny or making a funny noise, it's probably about time to think about replacing the lot. Receptacles that are loose from wear and tear can contribute to arcing and sparking conditions that can lead to fires and other scary experiences.
Calling in an electrician to replace these devices doesn't cost an arm and a leg. They can check out the panel box and make sure all the connections are tight while they are there. Who knows, they might just save you from a bigger expense down the road.