In the light novel, there are often deeper explorations of political and strategic aspects that might not be fully covered in the anime. Also, some character backstories could be more fleshed out in the book.
The 'How a Realist Hero Rebuilt the Kingdom' light novel offers a richer narrative experience. It can delve into subtler emotions and thoughts of the characters that might be hinted at but not fully expressed in the anime. Moreover, the pacing in the light novel can be more flexible to accommodate complex plotlines.
The light novel has more detailed world-building and character development. The anime sometimes has to condense or simplify for time constraints.