It's a temptation, especially when you have a big enough budget and a good will to help your overloaded software team. But at the end it maybe has the opposite effect.
A few disadvantages which just come to my mind:
- if the hard monkey job is done by somebody else you don't even start to think how to eliminate it (eg. module is automaticaly testable only if it's designed the right way)
- repetitive work is no fun - bad mood doesn't increase the productivity of your team
- the more people in the team, the more time spent in meeting, communication, management, administration...
If one succeeds in eliminating this repetitive tasks he/she is rewarded by having a smaller team which is more flexible, faster and most probably the deliverable will contain less bugs.
Let me put it simple: "Monkey tasks must be shared by the whole team, otherwise the senior people are not motivated to eliminate them."