Sage is primarily developed to support pure mathematics research (and undergrad teaching). Probably the main possibly unique thing Sage brings to numerical analysis is good support for arbitrary precision and interval arithmetic. Beyond that, Sage is written in Python, so it inherits the standard numerical functionality from that ecosystem, namely numpy, scipy, pandas, etc. Sage also has excellent support for Cython, since much of Sage is written in Cython (I even made up the name "Cython").