People can access your profile and vote on the different expertise and skills you have added. This lets users who are looking for them see how many people have endorsed you for a particular skills. It provides another indication on the extent of your capabilities at providing the services and help shared on your profile.
The votes are another indicator and work in conjunction with the rating which is different because it is obtained only on the service provided on Instantgo. Everyone can endorse your skills but only the people who have communicated with you on Instantgo can actually rate you (a transaction needs to occur).