You mean Theme Options panel? I am not sure if it is required, but how your clients will customize your theme without it?
Up untill recently, I would have said yes
But you really dont WP gives you everything need in the customizer IMO
If you think an admin area will help your particular theme however, then go for it! But be sure to add it for usefulness not just because everyone else does – no one needs a page full of options they just wont need
I can answer your question with another question: Does your theme really need an admin panel?
Sometimes it is not required at all or if the WP Customizer can cover all this. An admin panel is required if you add some functionallity to your theme, but sometimes these functions should be in plugins and never in themes. So think twice before making a decision.