Yes! When you create a product, the system adds automatically to the product autoresponder a message titled "How to access $PRODUCT_NAME$" (in Billing menu > Products > edit product > tab 'Autoresponder messages'). This message includes the login link, as well as the username and password for the client to login.
In cases where there is no need for someone to login (i.e. selling an ebook, a teleclass, live webinar, etc.), you can simply delete this autoresponder message. This will keep the client from receiving any login information.
*** Reminder: The system records the credentials for a buyer, even if you do not email them to the buyer. Also, the username & password will be needed if the same person purchases an additional product from you in the future. As recommended practice, an existing buyer should login before buying another product. Otherwise, if they buy again as new clients and use the same email address in the process of registering as new clients, the system will display a message informing them that they already have an account and invites them to login. If they use a different email address in the registering process, this will create a second account for them in your buyers list and you will perhaps need to merge the two accounts of the same person.
So, depending on how you want to go about this, you might consider adding a note in an autoresponder that is delivered at the first purchase where you remind the buyer to use their credentials to purchase future products and you give them the credentials using the replacement tags for the login link, username and password. ***