My grandfather changed his name and I wondered is there any information available as the reason someone might do this?

He was originally called George Jolley (born 1894 to John Jolley a Zinc Worker) but on George's marriage certificate to my grandmother in 1917 he calls himself Arthur Smith (with his father shown as John Smith a Zinc Worker).

My cousin (we share the same grandmother) told me that her father remembers my grandfather being labelled as "the black sheep of the family" - but no details as to why he had earned that title.

On his marriage certificate he shows himself as a "Tube Drawer" (in the gun industry) so I hope there was nothing sinister!! ...but if there was then so be it.

We originally thought that my grandfather changed his name because he had deserted the Army - however a very helpful member here (Retlaw) found my grandfather's army papers which showed he was discharged as "medically unfit" on 29/9/1914.

Any thoughts as to why people changed their name would be grateful and did they have to do it by deed poll and if so how could that be traced? Thank you.