Improve The Tone And Feel Of Your Instrument
Old rusty guitar strings never sound great, especially when recording. Old strings can affect the sustain and tone of the sound. It is recommended that guitarists change their strings before recording their instrument.
Don't Leave It To The Last Minute
I have always found it best to restring a guitar a good few days before the guitar is needed in the studio. Why? Well it gives the instrument time to settle and a chance for me to play in the fresh strings. The process of restringing a guitar doesn't just stop at putting new strings on... oh no. Strings need to be stretched in (played in) so that the tuning of the guitar doesn't become troublesome when recording. The intonation of the strings may need to be adjusted and even the tension on some guitars that have complicated tremolo systems.
It's Worth It
Queen's guitarist Brian May apparently uses old strings to the point that they break as he prefers the dull tone of used strings... each to their own I suppose. But he is an exception to the rule as he does play with a sixpence on a homemade guitar. However I'm trying to speak more generally here. Give yourself time prior to recording to change your strings. In experienced guitarists may need to get the instrument set up at their local shop.