Welcome to the forums, thanks for posting.
Yes, there are perks. You can gain up to 79 more players who may motivate or polish your buildings (on top of the people in your neighbourhood). You can also do 'guild trades', these allow you to trade within your guild without spending forge points. In the future, there are plans for inter-guild military actions, though no exact details have been announced.
Also, you will have people to talk to and enjoy the game with, as well as get advice from.
Hope this helps explain why being in a guild is a good idea.
While you're here I suggest getting acquainted with our lovely guides section where you'll find lots of helpful information.
Thanks for playing Forge of Empires.