Edward, Duke of York, as Earl of Rutland, was sent off to Guienne to act as Lieutenant during 1401-02, returning to England after the death of his father, Edmund of Langley. He claimed debts owing to him from the Crown as a result of this short period in office were not unadjacent to £10,000.
As mentioned in an earlier post, Edmund of Langley had relatively little land, and much of his income derived from Exchequer grants, some of which, admittedly, he had got assigned to reasonably stable sources such as the customs or wardships. Given the general state of Henry IV's finances - which a kindly soul might describe as critical - Edward's inheritance was not so shining a prospect as you might think. (The Exchequer being empty much of the time.) He also had a stepmother, considerably younger than himself, drawing dower from the York properties - she might be expected to outlive him, and as it chanced she did so by about 20 years.
Against this Edward had some lands of his own, notably the Isle of Wight, the remnant of the lavish additions Richard II had granted him. He also had his wife's life interest in the Fitzwalter and Golafre dower properties - fairly modest, but doubtless useful. He also had the advantage that none of his lands were in Wales, and so (unlike his sister Constance) he was pretty much free from the direct impact of the Glyn Dwr rising.
Edward clearly put pressure on King Henry for repayment of his alleged debt, one of the first fruits of which was the transfer of the wardship of Richard Despenser to the Duke of York. The previous possessor of the wardship was the boy's mother, Constance, and she had had a provision written into her patent that she was to keep the grant even if someone else offered to pay more to the King for the privilege than she did. I think we can safely assume she was not very pleased with her brother at this point!
Edward also (at some time around 1406) took over from Constance the lease of much of Elizabeth Despenser's dower lands, notably those in Glamorgan, including Caerphilly Castle. Apart from what was left to his sister in her own right by the King's grant, he was now in effective control of almost the whole of the Despenser estates.
Since Edmund of Langley had exploited the Despenser inheritance for so many years, it may be that his son saw it as something as a family tradition. He was to keep hold of the fruits of the wardship for the rest of his life. When Richard Despenser died, about 1413, the property ought to have gone to his sister, Isabelle, and her husband, Richard Beauchamp. However Edward simply petitioned the Crown for the right to keep hold of the Despenser lands, and this was granted. They passed to the rightful heiress only after Edward's death at Agincourt.
Towards the end of his life, Edward enfeoffed (that is, put in trust) many of his own York lands to pay for the establishment of Fotheringhay College. Given that he had no child of his own body, he was understandably more concerned about making provision for his soul than any impact on his heir. Given that his wife Philippa had to be dowered out of what was left, and that his stepmother was still enjoying her share, the remaining inheritance of the duchy of York was actually pretty modest.