Secondary fermentation

I have a quick question regarding secondary fermentation. Is it always necessary to put beer in a secondary fermentor and what is it's main purpose. Is it dependent on what type of beer you are brewing?
Thanks for the info.

nope its generally not needed. I only use a secondary for dry hopping (some use it for fruiting their fruit beers) secondary used to be primarily to get it off the yeast before it autolysed now its not such a worry. some people use it to improve clarity as well. personally I just run with long primaries and cold crash for clarity. I'm sure there are dozens of other uses that I havent typed out but some one else can list them, I havent had enough coffee for a dissertation.

I agree with Reef, fruiting, dry hopping or aging are the only 3 circumstances that I would use a secondary.

I use my secondary to let the beer clear as well. I usually go about 14 days in the primary and 14 in the secondary. Is it totally necessary, no. I just find that it lets the beer clear better.

I only use a secondary now, no primary.