Listen to Skeletor.
If you want a personal take on the matter, read on.
I had truly overdeveloped legs from the get-go, making my upper body look ridiculously small. It went so far that fully clothed, despite low body fat levels, people mistook my proportions for that of a 'big boned' fatty. No matter how lean I was: my legs were giving me more of an A shape instead of a V taper. But guess what? I was 16, not yet fully grown.
Here come's the precautionary tale: seeing how my legs were always big (and somewhat strong), I figured I could totally get away without leg training. What happened by NOT doing squat and deadlift variations was that my posterior chain was shit. My posture started to develop an anterior pelvic tilt with slouched shoulders. All of that might have contributed to me getting herniated discs many years later.
Sometime after that, I started training legs, more out of rehab considerations. Within just a few months of squatting and deadlifting, I made rather impressive progress, although I'd already been almost 10 years in the iron game.
- if your legs truly are big (or even over-developed), train them, but use low volume and / or low frequency as opposed to your other muscle groups
- grow a good pair of delts, don't neglect the lateral and posterior portions
- grow big and thick lats
- keep that waist in check, body fat - wise