Why are BED files necessary for somatic calling?

Question

[vctrm67]

Apologies if this is an elementary question, but why are BED files necessary (if at all) for somatic mutation callers, other than to simply speed up the calling by restricting calling to certain regions? I see an option to specify calling in certain regions. Does it actually improve the calling sensitivity/specificity at all?

[ATpoint]

No, these files are not necessary but typically can be used to specify regions in order to reduce runtime.