I could think of a number of scenarios.
1.Say, in future, for example you want to offer shares from one your division, ABC Contractors which is a subsidiary of ABC Holdings offers share for partnership with someone with experience or vast knowledge and network in construction. But you don't want them to have any association with ABC Cleaners or ABC IT Solutions.
2. Protection of your other business, should there be a legal dispute
It's quite a lot of administration. If I decide to use just one company for everything, won't it affect records? Cause then it'll be like you forming a new company e.g. ABC Contractors, should I decide to only register that company independently when it's a large company