Is necessary to have a guide to see The Uffizi and Accademia?

Absolutely not if you're willing to read a few guidebooks ahead of time and do some research.

We took Rick Steve's "Mona Winks" when we went through the Uffizi. It's useful for anyone who hasn't studied the history of art--as well as for someone who has but who needs a refresher. It tells you enough about certain specific pictures that you can place them in a historical or artistic context--without weighing you down with too much information.

no not necessary. but definitely worthwhile.

I found the audio-guide at the Uffizi very helpful.