This is an extremely serious thread. The likelihood of having a problem with a trailer (forgetting to lock the hitch, attach chains, raise stand/wheel, flat tire) rises exponentially with frequency of use. (This is true of most dangerous activities.)
If you are running a professional business, you should have professional tools - including your trailer. Even though you may normally not overload -or even load to capacity - your trailer, the day will come when you need to carry water to a site and every gallon weighs 8.33 lbs. I have a 300 gallon tank (8.33 x 300 = 2499 lbs). Add that weight to the actual weight of the trailer and all of a sudden, you could have almost 2 tons of extra weight to stop. Your truck/van will most likely stop, but it will stop sooner if your trailer has brakes.
(While we're on the subject, tongue weight should also be taken into consideration. Also, prior to leaving every job - or starting out in the morning - my company policy is to test the trailer lights.)