When verifying trigonometric identities, it's generally a good idea to get everything in terms of sine and cosine. That's not always the case, but many times it's helpful.

Remember that sin^2(x) + cos^2(x) = 1
                         1 + tan^2(x) = sec^2(x)
                         1 + cot^2(x) = csc^2(x)

csc(x) = 1/sin(x)
sec(x)= 1/cos(x)
tan(x) = sin(x)/cos(x)
cot(x) = 1/tan(x) = cos(x)/sin(x)

Because all the trig functions are based off of sine and cosine, you can clearly see why this would be a benefit when verifying.

It's also a benefit when solving trigonometric equations.