Convert Color

[FAMOsa]

I have been using gimp to manipulate images of my paintings.  I take a picture of the painting with my iPhone, convert it to JPEG, and then upload it to gimp to straighten, crop, etc.  It always asks me if I want to convert to to sRGB or something like that.  The default is to convert, so I do.  However I was wondering what the difference was and/or if there is a tutorial that teaches what these conversions mean and how to choose the best options for your project. 

Thank you in advance.