How do you use the phrase 留宿 （liu2su4） （i.e. “To stay over at someone's house") I've been trying to figure in what contexts it is appropriate to use the term 留宿。
Is it simply staying at another person's house for the night (like in english "crashing at someone's place") or is it a bit more formal than that? 
For example, could I casually tell someone in a new city I am in. 

"今天我打算在李雷家留宿？“
Yeah it's kind of formal and "old-fashioned".

Expressing 今天我打算在李雷家留宿 more naturally can be 今天我打算住李雷家 or 今晚我打算住李雷家.

今天 in this sentence implicitly means 今晚 (tonight).