Civil defendants in federal court are obliged to waive service. All of them, with the notable exception of various governments. I give you Rule 4(d)(1):
An individual, corporation, or association that is subject to service under Rule 4(e), (f), or (h) has a duty to avoid unnecessary expenses of serving the summons.*
(Emphasis added.) Seems pretty simple to me.
Continue Reading Rule 4(d) waivers and fee shifting