Reasons to outsource include; 'overheads can be kept as effective as possible' and 'the reduction in the need to continually invest in new machinery'.
When you outsource, you transfer the costs of overheads to the supplier and it is their responsibility to buy new machinery as and when is required. For example if you outsource cleaning, the cleaning company is responsible for replacing the hoovers and floor cleaner The other two options would be reasons to keep something 'in-house'.