First of all, I want to explain for everybody what does odex/deodex mean. These terms are oftentimes used when talking about Custom ROMs. A lot of Mods have the condition to be used with Deodexed ROMs and a lot of new Android users have no idea what that means. So I believe it is important to explain to everybody what is an Odexed/Deodexed ROM. In the last part of the article I will explain Odex vs. Deodex and what are the advantages and disadvantages of each type.
What does Odex mean?
When you hear the term 'Odex' it refers to the extension (.odex) of certain files. What files am I talking about? Well, Android system apps come in packages with the extension .apk, here the term 'APKs'. They are Android applications contained in one single package. These packages have .odex files which are originally meant to save space. Their purpose is to contain some parts of an application that will further on be optimized before booting. This makes the loading of an app a lot faster because these .odex files are preloaded.
For developers, .odex files are difficult to hack. That's because the purpose of the .odex files makes them reload into another location before running. That's why they created the deodexed (or de-odexed) files.
What are Deodexed files?
Developers are repackaging all the APKs into a new form of files extended with classes.dex. This unites all the parts of an application and eliminates the conflict between a modified APK and other .odex parts that are separate.
By uniting all APKs in one place, Custom ROMs become a lot easier to modify and customize. That's why developers almost always deodex the ROMs that they are working with.
What are the advantages and disadvantages of Odex and Deodexed ROMs?
Odex vs. Deodex: The main advantage of deodexing a ROM is to make it easy to customize and modify. After deodexing a ROM, a developer can add themes and modify apps at all times.
On the other hand, deodexing a ROM will increase the initial boot time. However that will only happen on the first boot. After that only a Dalvik Cache wipe will make the initial boot take a lot of time.
So in conclusion, Deodexed ROMs bring more advantages than Odexed ROMs. Usually only stock ROMs are Odexed, because almost every developer out there chooses to Deodex their Custom ROM.