People who have done their schooling from any school in Delhi come under Delhi, otherwise outside Delhi.

Since GGSIPU is Delhi govt funded university, it has seats reserved for the students from Delhi region. That is all as far as difference goes.

Also, outside Delhi student will need to get a better rank in order to get same college as Delhi student with a lower rank comparatively.

If you have done your schooling from delhi , then you are considered from delhi region and if not , then outside delhi .Also , outside delhi region includes students from outside indis but all india region includes students only from india . Also delhi region students have a state quota.

Hope you got my point .