+1, always do this... I tend to find that certain design constraints need breakpoints that don't match the atypical @media breaks that are used in Bootstrap and the like... just by nature of what's being placed... It's best to actually exercise and practice where you're breaking things down.
Also, since I tend to use React/Redux lately, I inject size/scroll into my state and use that as a basis for those decisions in controls as often as I'll use CSS/JSS alone anymore.
That's what I do when I'm making a responsive website - I'm constantly changing browser width to make sure it works at all sizes.
It's not enough to just check for the @media sizes - you also need to check the sizes in between in case boxes get shrunk too small to fit their content.