Wife name changing :consequences

Advantages:  You are following the tradition that wife's surname should be that of husband's after marriage.  You will not face the questions from your children about different surnames of their parents. Moreover both of you feel united after marriage.

Disadvntages:  As you are planning to change all the documents, there are no disadvantages.  However, if you do not change the surname in her education certificates, sometimes, she may face problem at the time of certificate verification.  You can overcome this problem by producing marriage certificate. 

Wish both of you all the best!

normally after marriage in our hindu tradition wife surname of her father will be changed to husband family surname and where ever it is requied you can give a formal letter stating the marriage details if you do not have marriage certificate and change accordingly and if you have marriage certificate the procedure will be same enclosing the marriage certificate

and about disadvantages i dont know any thing

No need to change her name in Educational Certificates. As understood, I think you are from Andhra Pradesh. First you shall approach Government Printing Press in Chanchalguda, Hyderabad and get proper application from District Collectorate or if you do not have obtained the application then you can secure such application from Government Printing Press. You shall pay requisite fee and mention the reason for change of name. Later submit that application and her name gets changed and it will be printed in Government Gazette and a copy will be sent to your address. Keep the GO along with you and change her name in all documents but regarding changing in educational certificates is risky...

he wants to change only surname not her name 

for example Ms. Swathi xxxx  is her original name and after her marriage with Mr. yyyyy Anand means automatically wife name and her surname will change to Ms. yyyyy Swathi and were ever she wants to change a formal letter and if she carries marriage certificate is okay and

Ms. Swathi wants to change her name to Ms. Anushkha then the above procedure is applicable 

and about educational certificates in our legal system once after marriage there is no such clause that wife should change all her educational certificates with her husband surname