When a company keeps some stocks reserved under the shareholding quota, investors who hold at least one share also come under this quota and they can take advantage of this category. Usually, subscription under shareholding quota is much lower than other categories such as retail.
The second benefit is that when the IPO of a subsidiary company is announced, you can apply through 2 separate applications – one under retail category with a capping up to Rs. 2 Lakhs and the other under the shareholding category with a capping up to Rs 2 Lakhs. Applications under both categories will be considered valid. So in such a case, you have a better chance of allotment when the subscription goes above the required limit.
Lastly, companies usually offer special discounts under shareholding quota. In such a case, you will get some special benefits when you get allotment under the shareholding quota.