Auto created Statistics vs Manually created Statistics
The only major difference is that SQL Server will only ever create single column statistics. You can create multi-column and filtered statistics. If any of the statistics you created were those types, they may be important. If not, SQL Server is likely to have created system statistics on those single columns, when deemed useful to a query. 

Unfortunately you have to do a bit of digging to figure out which statistics your queries are using. 

See here for checking the plan cache. 

See here for checking queries as you execute them.  Note in the comments that on 2014+ you require a different trace flag.