pg_stat_all_indexes understand

Hello,

I wonder how understanding pg_stat_all_indexes working

When I run an explain, some index are not used, but
pg_stat_all_indexes.idx_scan is incremented for those indexes.

Does this mean idx_scan is incremented each time the planner check if an
index could be use whenever it won't use it ?

Is there a better way to check which index could be delete ?

Thanks by advance.