What are the negative and positive consequences of a system of seperated powers?
The United States Government consists of a separation of powers (3 branches of government). What are the positive and negative consequences of the separation of power?
The consequences of a separation of powers are that it increases the consistency of a government's policies as applied across various individual cases. It increases the level of agreement needed to go through with government action (like putting someone in prison). I disagree with user4012 that it inherently takes longer to come to a consensus. A council of 3 in a state without separation of powers can take just as long as the heads of 3 branches. Read more here: https://governology.wordpress.com/2016/04/12/dimensions-of-government/
I won't bother providing quotes, but you will find the reasoning behind such an organization of government in the writings of US Founding Fathers, specifically in Federalist papers — as well as those who influenced them (e.g. Locke here), as well as French Revolution (see the short writeup on Wiki on Montesquieu's tripartite system ), though the system's origins lie in Ancient Rome and even Greece.
The short short version is that such separation promotes what's known as "Checks and Balances"— it allows the power of one side of the government to act as a counterbalance and a check on the power of the other ones, thus preventing either from becoming a monopolist of power.
The negative consequences are that in emergent situations, you end up wasting time building consensus and such. In some cases this is very bad and dangerous (e.g. being militarily attacked), which is why US adopted things like limited-time-warfare by Excecutive branch (supposedly, checked by War Powers in theory), so that the Executive branch can decisively mount short term and timely military response to international national threats. This again goes back to Locke (“the power of doing public good without a rule”).
Wikipedia has further mentions of various perceived pros and cons, such as various views on emergence of influence group politics, judiciary's independence etc. I'd rather not copy/paste Wikipedia for those.