Two concrete wins. First, zero runtime cost: anything computed at compile time, a derived baud-rate divisor, a CRC or sine lookup table, a gamma curve, costs the device no cycles, because the compiler did the work and the result is a constant in the instruction stream or a pre-filled table. Second, memory placement: a constexpr/const table with static storage lives in .rodata, which is mapped to flash, so it consumes no scarce RAM. The alternative, computing the table at boot in a runtime loop, costs both boot-time cycles and RAM to hold it. On a part with 20 KB of RAM and 256 KB of flash, pushing constant data into flash and eliminating boot computation is a direct, measurable resource win. It's the C++ way to get the benefits of a hand-maintained const table without hand-maintaining it.
C++ for Embedded · Interview question
Why is constexpr especially valuable on a microcontroller?
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From the lesson
const Correctness & constexpr
const propagates read-only intent through your whole API; constexpr moves computation to compile time so lookup tables and config land in flash with zero runtime cost.