What special privliages did scribes have because of their social position?

It would depend on which societies were being asked about.

In many ancient civilizations, the scribes were really the only people that could genuinely read and write in the complicated, robust, yet still primitive forms of language that existed.

Cuneiform for example, originally was created as a means of tracking trade goods, debts, accounts to be paid and so on. It was the heart of the trade system, so not only were the scribes literate, but they were also Accountants. These positions were incredibly valuable and important because without them (or with a dishonest scribe) things could quickly go awry for a government or merchant.

Most early language systems (especially in writing) were also a very elaborate system, which used different symbols for each type of item and quantity, sometimes created rather randomly and without cohesive form. The scribe couldn't 'figure out' what something meant, he had to 'know' what it meant for a fact and be able to recall and work with that item intellectually.

On top of all that, the scribe had to be able to write or draw the Words and letters that signified the contents and status of goods, sometimes into wax seals or clay tablets, meaning they had to have some degree of artistic talent as well.

In civilizations that worked under such circumstances, scribes were held in very high regard indeed, both because of the inherent talent and intellect it took to hold the position, and also because of the power and potential abuses of a scribe. A trustworthy and talented scribe was an absolute must for a powerful merchant or government and as such, they were highly sought; and they were treated accordingly.

It may well have been one of the most revered non-political and non-religious positions in all of human history.

What individual social privileges this enabled scribes to have varied based on who they were employed by, what specifically they were tasked to scribe (laws and religious documents were far more important than a record of a traded pig for example), and what their quality of work was.

It would also have been based on the culture of the society and the particular time and place of the society that particular scribe worked in.

The privileges ran the gambit in many different cultures depending on the setting. They could have been granted everything from a simplistic salary to access to concubines, palaces, land of their own, a voice in leadership of a civilization at the highest levels, or at times entombment in the temples of the greatest of their civilization's leaders.

Their 'perks and benefits' really ranged the entire spectrum of potential reward, depending on the time and place they lived.

Suffice it to say that they were very valuable people historically, and they were treated accordingly.