You 'probably' don't need one but 'should' use one to save yourself countless hours re-inventing the wheel that frameworks solve.
The best thing is to try and use minimal frameworks and libraries and justify every single one - Which I'm sure most devs already do. jQuery is still rather justifiable. Yes, you can replace functions with JavaScript today but you'll end up with similar looking functions.
I recently added Transit to animate using CSS3, the alternative would be to write each animation effect I use in CSS3 down to the duration! If I need to change the ease I spend 5x the time doing so - From a devs perspective no, just no.
The best thing is to try and use minimal frameworks and libraries and justify every single one - Which I'm sure most devs already do. jQuery is still rather justifiable. Yes, you can replace functions with JavaScript today but you'll end up with similar looking functions.
I recently added Transit to animate using CSS3, the alternative would be to write each animation effect I use in CSS3 down to the duration! If I need to change the ease I spend 5x the time doing so - From a devs perspective no, just no.