When performing nodal analysis, should you simplify a circuit first?
The maths works the same in either case, as long as you keep track of all the variables and signs.

We humans tend to 'simplify' groups of components when working by hand, because it reduces and organises the arithmetic workload, and our visually oriented brains work well picking out patterns of components that will simplify. 

We program computers to just mash the entire circuit as is, because it's easy to program them with a general matrix method, it's difficult to program them to group and simplify components and take advantage of the reduction, grouping components loses information that might as well be kept, and the difference in execution time is negligible.

Compare how we were taught to do simultaneous equations in school - recognise the most convenient factors of one of the variables in the two equations and cancel them - and how we program that into a computer - fill in the 2x2 matrix, invert, multiply by the 2x1 vector, regardless of the 'shape' of the problem.