What happens if we use same WiFi name for both of the bands?

no, it will work fine.

there is no issue in that its gonna work fine.

Nothing is going to happen, devices and router will work fine

Nothing will happen if we use same WiFi name for both of the bands.Router will be working fine.

you might face issues related to the connectivity or speed into the home network

nothing is going to happen, devices and router will work fine.

but yes, it might gives you trouble with few devices(for example:- temperature sensor ,wifi enabled door bells or ip cameras)

the devices compatible with 2.4G band will connect to the 2.4G band and the devices compatible with 5G band will  connect with it.

The devices which are compatible with the 2.4G they gonna connect with it and if devices are compatible with the 5G they gonna connect with the it.