The idea here is to pre-simplify complex areal or lineal geometries with a topology aware methodology before their vertices get translated into the lower resolution coordinate space of a tile. The goal is to avoid invalid geometries as much as possible.
Generally:
A best fit value for simplification is a function of geometric composition, complexity, vertex count, distribution and segment length - all unique to the geometries in question; to get a more general feel for the possible input values, I would suggest to establish an understanding of the effect of varying ε (epsilon) values in the Ramer–Douglas–Peucker algorithm.
Specifically:
If the SIMPLIFICATION flag is set to a value > 0, the OGR MVT feature generator¹ of the parent MVT writer class² applies the GEOS TopologyPreservingSimplifier algorithm³ on the intersection of a given (areal or lineal) geometry with the given tile bounds⁴, using a distance tolerance factor of
TILE_DIMENSION_AT_0 / 2^ZOOM / TILE_EXTENT * GIVEN_SIMPLIFICATION_VALUE
where
TILE_DIMENSION_AT_0 defaults to 40075016.686 (derived from the default tiling scheme for Web Mercator⁵; given in meter)TILE_EXTENT defaults to 4096
¹ code reference
² code reference
³ code reference
⁴ code reference
⁵ code reference
