does clearing thumbnails in phone has any effect on a phone?? Thanks for your humble replies

When you delete thumbnails, Your phone could be slower in finding and displaying pictures

Thumbnails are stored in your phone's cache which is stored in your phone's RAM memory.

In theory, if you clean your phone's thumbnails, the cache and RAM memory should cleaner and less used, so it should run faster.

Its totally safe
thumbnails are created for faster opening of gallery otherwise the RAM has to load all again.. But if you want to you can delete!

https://www.asus.com/zentalk/ph/thread-80741-1-1.html