If you are in insert mode and typed a command for normal mode, you can use it.

inoremap <somekey> <Esc>u@.

This mapping switches to normal mode, undoes the last insertion and takes it as a command.

Most times I need it, if I typed dd and the line still remains because of Insert-Mode and the unwanted 'dd' ist somewhere in my text.

Comments

I guess you meant:

inoremap <somekey> <Esc>u:@.

I prefer

inoremap <somekey> <Esc>u@. i

Also

yy@"

Explanation:

yy yank current line into default register
@" execute default recording