"obvious purpose" is correct and usable in written English.
You can use it to refer to something that is clearly and easily understood. For example: "The teacher's obvious purpose was to teach the students a valuable lesson."
But often the thread is lost in a jumble of information without obvious purpose.
Others, like the Congressional Songwriters Caucus, have a less obvious purpose.
"The obvious purpose of the procedure is palliation and symptom relief.
Minions with an obvious purpose, sectional game-play and a wide range of dynamic, specialised characters.
It described the Democrats' "clear and obvious purpose in proposing, passing and implementing socialist programs through federal legislation".
There are also extended passages when the matronly Lepage moons around the stage in powder and mobcap to no obvious purpose, recalling decades-old performances by Lindsay Kemp.
Lost, apparently, on Burton was McNamee's stated and obvious purpose for lying, to protect Clemens, until he was trapped into the truth by the Mitchell investigation.
However once Ms Desai made it clear of her wishes, the repeated texts, emails and even alleged visits to Ms Desai's home address serve no obvious purpose.
Despite their obvious purpose -- which more than likely has something to do with a parade or a contest -- they have all been made to feel extra-special.
That's usually a clue that one piece has to perform more than one function, sometimes a function unrelated to its obvious purpose.
Like the comers and goers who jump into Robert Pattinson's limo in Cosmopolis, they serve no obvious purpose other than to share and extract deep thoughts.
