What the numbers are doesn't matter, the solver uses iterative algorithms that save inverting the whole N x N matrix. Matrix operations are O(N^3), so a modest circuit with 100 nodes takes about 10^6 more operations than a basic battery and lightbulb circuit. And that's if it guessed the correct timestep the first time, which very rarely occurs. SPICE throws away a
*lot* of computation.Obviously, you've never simulated anything of significance, or you'd know this. The degree of these approximations is controlled by the simulation parameters, which experienced users understand must be optimized for a given model to avoid slowing to a crawl (with default settings, LTSpice likes to wander off into the picoseconds, eating glue) or generating errors (most often "timestep too small").
Tim