Yes! Promoting your Heroes to Emerald gives them the benefits of Rank Promotion along with the ability for you to make your own custom Level Scaling Stat boosts.  There are a few things to keep in mind:

Stats from Badges still matter a lot:

• Not promoting your Heroes means that you'll miss out on the powerful badges from higher Ranks.
• This will add up pretty fast as more Emerald Ranks release month over month.

For a lot of Heroes, Emerald is the best way to gain access to powerful Level Scaling Stats:

• There are many Heroes in the game that don't have the best access to Level Scaling stats.
• Promoting them to Emerald allows them to get these powerful stats and maintain them.
• Emerald also affords you the ability to choose which stats you think work best for your Heroes.

Long-term Maintenance:

• The long-term maintenance of Level Scaling Stats have primarily shifted into Emerald Ranks.
• Since these stats are no longer provided by Badges, any effectiveness of a these stats that come solely from badges will diminish over time as more Team Levels are added to the game.
• This means that for most Heroes, the only way to continually gain these Level Scaling stats will be to promote them through the Emerald Ranks.

Ambition is a double edged sword:

• It's true that if you leave your Heroes at Y+30 then all of their Level Scaling stats will ignore the Ambition of your enemies... which on the surface seems tempting.
• However you should keep in mind that your Heroes also will not have Ambition which could prove to be problematic.
• For example let's say an enemy Hero has 2 effective Level Scaling stats and then promotes to Emerald.
  • That enemy then chooses two other Level Scaling Stats for their Subclass.
  • During combat, that enemy will now have 4 Effective Level Scaling Stats against your Y+30 Hero.
  • If you promote your Hero to Emerald, the enemy would then only have the 2 chosen Level Scaling Stats that will be effective against your Hero.