OBJ export stores (often bogus) texture coordinates of boundary halfedges
When exporting a mesh as OBJ, unused boundary halfedge-texcoords are stored. They are not used anywhere and the resulting file seems valid. However if those stem from uninitialized memory, the number of different texture coords can significantly bloat the .obj file size.
Example .obj excerpt
vt -76500107434139575140676561222651346944.000000 1.970980
vt -4950073864930567497435155906561048576.000000 -1.834825
vt -1931694947632209777361309154513256448.000000 -1.832364
vt -1238546134728614397081714835220070400.000000 1.814589
vt -707588858575282684185056046137475072.000000 2.654118
vt -73317830722383046556445364377878528.000000 2.735005
vt -19543880572954837544928206655586304.000000 1.928249
vt -3437403581334206476565834471833600.000000 1.928330