This is the part most vendor content skips, so it is worth naming directly.
In-house cleaning gives you direct, day-to-day control over the person doing the work. If something needs to change, you can say so in real time. With an outside provider, you are working through a contract, a scope document, and a point of contact. Communication has to be more deliberate, and there is an adjustment period as the crew learns your building.
For some operations, particularly those with highly specialized environments or very tight oversight requirements, that tradeoff is significant and worth weighing carefully.
It is also true that not all outsourcing janitorial services relationships work the same way. Providers that assign a consistent cleaning team to your facility, conduct regular inspections, and maintain open communication close that control gap considerably. Providers that rotate crews constantly do not.
The quality of the outsourcing relationship depends almost entirely on the provider you choose.