Portability is a thoroughly modern estate tax break -

Computers and phones aren’t the only things that are portable today. The gift and estate tax exemption is also “portable” for married couples. Portability simplifies estate planning by allowing a surviving spouse to use the deceased spouse’s unused portion of the $5.45 million gift and estate tax exemption amount. This means that married couples can maximize the benefits of their combined exemptions without the need for sophisticated estate planning involving multiple trusts...