An apartment walkthrough is a process of going through an apartment to make sure everything is in good shape.
Both the landlord and tenant need to participate and a walkthrough should be done before the tenant moves into the apartment.
An apartment walkthrough is beneficial to both the landlord and the tenant. It protects the tenant by informing the landlord of issues that exist before they move in, so the tenant won't be stuck paying for repairs on things that weren't their fault.
It helps the landlord to keep the apartment in good shape and avoid angry tenants down the road.
There really isn't a good reason why you shouldn't do an apartment walkthrough. While it's helpful to both parties, it'll be most beneficial to you as a tenant, and it will help you take care of things that could have been issues for you later on. If your landlord doesn't offer to do one, make sure you ask about it.