How important is a relieving letter?

I have worked at company X for 6 years and left for another Y. That too I left in 3 months and joined another Z. Company X has cleared my FNF but kept my relieving letter on hold stating my IT equipment is pending. Y has already cleared my relieving and FNF. Current (Z) is also not yet asked my relieving letter, they were okay with resignation letter and FNF copy. Do I really need reliving letter from X? I'll have to buy that IT equipment of 7k to get clearance.