Most people will already know that from the beginning of February, Apple’s Mac app store will require all new submissions to support 64bit. Previously uploaded apps, created for 32bit would have a grace period of 5 months and would need to begin supporting 64bit by June this year.
For developers planning on distributing apps outside the App Store, it is recommended they work in 64bit binaries to make sure the apps run on future versions of iOS. The last thing anyone wants is compatibility issues. The best way to build and submit an app is using Xcode 9.2.