I think i answered to your question already 21 days ago on another post (from you..) :)
you answered also yourself in the question by saying "except user interface and the look", yes, but it's mostly the reason for which you can buy different phone on android for example. Some may prefer Samsung design than Huawei, other just prefer iOS and Apple. After all it's the same use : phone calls, sms, internet, apps. So what's the benefit ? Offer different choices for different people/vision. And yes, the user interface/experience and the look does count ;)
Thanks again, guys! This completely answered my repetitive question =D
I would say that for example steemit.com is to be considered a form of "open contract", that relates to a resource (The Steem blockchain).
You as a user can choose to use (sign) this open contract/steemit.com in order to access the Steem blockchain. If you want to and support it's maintance and developement.
By using steemit.com you accept the rules regarding passwords that most likely were displayed to you when you signed up ("The first rule of Steemit is: Do not lose your password") and up until recently there was also an info box for downvotes ("flags") on this user interface/contract, that informed you about what the "flag" ought to be used for.
... Now Busy, is another contract, where certain features such as flags/downvotes/smileys/goofey effects may have been removed/added to make things better for you as the person "signing the contract" each day by using the platform to access the blockchain. When using Busy, you don't need to consider any rules/guidelines given by Steemit.
Ultimately, it's up to you what platform you want to you use - or open contract you want to sign, so to speak.