First, an ideology is a worldview in which the conditions of that worldview prescribe structures, individual roles and social organizations which reproduce those same material conditions of that worldview. What this means is that an ideology is the structure of ideas of the way society (or the world) can, does or should function; and that structure of ideas, etc. is the means of reproducing that ideology. In other words, an ideology is not just some collected ideas. Put into practice in the structure of a society, the material conditions created therein actually reinforce the ideas of that ideology. So, if part of an ideology is that the son of a farmer should be a farmer, the son is likely to become a farmer. This is an obvious example where an ideology can condition the very livelihood and lifestyle of an individual.
Ideologies can be very complex and interwoven in all aspects of human life. But they can also be simple descriptions of how a society is or how it could be.
The benefit of ideological reasoning is that it provides a simple understanding of how a society functions. (This is also a danger because the oversimplification can beget citizens to passively accept the dominant ideology.) However, on the other hand, another benefit is that an ideology can be presented in order to change society. As this can be for the better or for the worse, it all depends.
In general, the use of ideological reasoning is that it is a deductive approach that analyzes our beliefs, roles, social structures and then it is an analysis of the ways we put those beliefs and roles into practice. In short, ideological reasoning is an analysis of how we live, or how we could be living.
The first risk of ideological reasoning is that the logic of an ideology is mostly self-contained. That is, something outside of that ideology that conflicts with it would seem illogical. However, it is only illogical with respect to that ideology. That sounds a bit redundant. All it means is that the reasoner should always be aware that the logic of an ideology is largely particular to that ideology. To think outside the box, the reasoner should always be aware there are other ideologies, other worldviews which may expose the lack of logic of an ideology.
Another risk of ideological, deductive reasoning, is that it begins with the core beliefs and then proceeds to particular ideas and material manifestations of those beliefs. Beginning with the general beliefs can frame those particulars in terms of those beliefs. Thus, the reasoner might intuit that all practices are justified. Rigorous ideological reasoning might avoid this risk, but it would be better to supplement an ideological analysis with some inductive reasoning. This would be looking at the particular ways we think and live before we look at these general, broad beliefs. This might help avoid some unconscious acceptance of some unethical practice simply because it fits nicely with an otherwise, seemingly just ideology.