[BScout]

Originally Posted by jd1234

Can anyone here explain the drawbacks of using the clock of an external device? For example, i just started using a Apollo Twin X Interface (Thunderbolt) and i have it set to use the internal clock. So i believe (not a 100% sure) when i am using the Apollo with Pro Tools I am using Apollo's internal clock when recording.

Yes.

Originally Posted by jd1234

I am thinking this may end up being a problem if I am going to eventually have someone else mix my project. Won't he need the Apollo interface if he wants to sync to the clock that i recorded the tracks on? Same thing with sending my pro tools session to other musicians to lay down parts.... won't they need the Apollo if i am using the clock in it.

No to all of this. That's not how a sample clock works.

Originally Posted by jd1234

By contrast, if i use Pro Tools clock than it will be very easy for anyone with pro tools to open the session and lay down their part, mix the album on their gear, etc.

No such thing as a "Pro Tools clock" in native Pro Tools. The "clock" is whatever your audio interface that is set as the audio hardware for Pro Tools.

Originally Posted by jd1234

Is my understanding of this correct?

Nope. Not in the least.
Basically, don't worry about it. If you have only the Twin, then internal is the correct setting and don't think any further about this.