Any Syncrhonization License gives you a 'credential' to refer other companies or Music Supervisors (a.k.a. Broadcast Producers) to as samples of your work.
Other 'sources' where they can hear product are also of value too. They're looking for product. They're always in a hurry with deadlines of their own. Success breeds success.
Owning your Copyright and Master Recording enables you to go 'All In', able to contract for a 'use' of your product without complications from co-writers or Producers who claim ownership of the Master.
These legal formalities are simple when all depends on your signature alone. Consultation with a lawyer is always advisable when signing your name.
Ideally the contract will specify the duration of the 'use'. It is only a 'use', usually for a specified period, at which time you are free to market your Intellectual Property for other 'uses'. Some may specify that you're free to market it for other uses, as long as it's not something competitive with the first 'users' market.
Movie 'uses' may be different, intending a permanent 'use' if the movie's a hit. Depending on what the contract specifies your ability to market that composition for other 'uses' may be limited or wide open. I recommend getting the contract to say what you want it to say. They'll get it to say what they want it to say. Somewhere in the middle should be a reasonable compromise satisfactory to both parties.
Don't...Do not...interrupt a process already in motion. Nothing gets you a worse reputation than complicating things after the person you've been dealing with has gone to her boss, his boss, and told them everything's a 'Go!'
Getting the 'credential' of a 'use' now is more valuable than getting the contract just right. It's a learning experience for the next contract.

There will always be another song to be written. Someone will write it. Why not you? www.garyeandrews.com