Indicators 'attached' to a chart & including & embeded in the EA - vs - making an 'external' call to them?

[FourX]

Howdy All,

From what I have read, one doesn't HAVE TO include indicators within the EA nor even attached to a chart in order to utilize them, but can make 'external calls' to them when needed.

I'm wondering about the 'Pro's & Con's' and 'trade offs' of these two different methodologies?

Thanks to any and all for your thoughts, knowledge and assistance with this!