A lot of musicians do not insurance their equipment, some believe they are careful and vigilant enough that their beloved equipment will not get damaged or stolen. It is certainly good practice to care for and cherish your instruments, and simple steps to keep them safe such as always using a dedicated hard case, never leaving the items anywhere they can be stolen and keeping the instruments out of the hands of children.
However, all it takes is one lapse in concentration and it could lead to a very expensive mistake. Guitar straps have been known to break and the instrument falls to the floor, you may slip while carrying your beloved trumpet or get over enthusiastic and push your foot through the bass drum.
If you have no instruments because they are stolen or damaged beyond use then you will have to beg, borrow or steal in order to play that lucrative gig you have been offered. By insuring your instruments you are will be confident that they will last you your entire musical career, or until you want to replace them with a newer and shinier model.