日本語
しなくもない
ここにあるように、二重否定 (a double-negative construction)であって、確信性が低い (to say something less confidently), or しぶしぶ認める (to reluctantly admit something)ときの表現で間違いありません。
それ以外の解釈を加えますと、この表現は会話の中でよく使われます。この表現が比較的よく使われる理由は、この表現は、「確信性が低い」「しぶしぶ認める」という論理的な意味合いで使われる以外に、「持って回った言い方 a roundabout expression [way of saying] 」あるいは「どうとでも捉{とら}えられる ambiguous」表現であることから、日本人の意思表示の典型的なスタイルである「明言を避ける to steer clear of definitive commitment」あるいは「あらかじめ逃げを打つ to (prepare to) run away (from one's responsibilities, etc.)」のに大変便利な言い回しだからだと思います。
English
しなくもない
As is written here, it is a double-negative construction, which can be seen as a set phrase used to say something less confidently, or to reluctantly admit something.
If I add another interpretation for the expression, I could say it is often used in conversation.
Other than the reason that this expression is used relatively often with logical meaning like to say something less confidently or reluctantly admit something written above, it is a very convenient way "to steer clear of definitive commitment" or "to (prepare to) run away (from one's responsibilities, etc.) which is a typical style of Japanese manifestation of their intention, because the expression is "a roundabout way of saying" or "ambiguous".