These days mobile phones come with support for different sim types. it either supports the mini-sim (a.k.a the standard sim), the micro sim, or the nano-sim. this can be a challenge when moving a sim card from one phone to another during travels or emergencies. a sim card adapter can solve this problem.
without a sim adapter, you have to look for a phone that supports exactly the same sim type as your own phone, which could be an uphill task. sim adapter makes switching sims more convenient and is recommended for anyone that owns a smartphone with nano sim or micro sim support